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BGCSE Physics 1427 study materials
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BGCSE Physics 1427 practice questions

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Question 1Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

Which of the following quantities is a vector?

  1. Speed
  2. Distance
  3. Mass
  4. Force Correct answer.

Explanation

A vector quantity has both a size and a direction, while a scalar has size only. A force is a push or a pull acting in a definite direction, so it must be described with direction as well as magnitude. Speed, distance and mass are each fully described by their magnitude alone.

Question 2Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A car travels a distance of 100 m in 20 s. What is its average speed?

  1. 2000 m/s
  2. 5 m/s Correct answer.
  3. 20 m/s
  4. 0.2 m/s

Explanation

Average speed is the total distance travelled divided by the total time taken. Dividing 100 m by 20 s gives 5 m/s. The value is an average because the car's instantaneous speed may rise and fall during the journey.

Question 3Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

Which force acts between two solid surfaces in contact and opposes their relative sliding?

  1. Friction Correct answer.
  2. Upthrust
  3. Air resistance
  4. Tension

Explanation

Friction arises where two surfaces are in contact and acts along the surfaces, opposing relative sliding or attempted sliding. It therefore points in the direction opposite to the motion or the intended motion of the object.

Question 4Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A beam is balanced on a pivot. A load of 40 N hangs 0.50 m from the pivot on one side. At what distance from the pivot must a 20 N force be applied on the other side to balance the beam?

  1. 1.0 m Correct answer.
  2. 0.25 m
  3. 0.50 m
  4. 0.75 m

Explanation

For a balanced beam the total clockwise moment about the pivot equals the total anticlockwise moment. The 40 N load gives a moment of 40 × 0.50 = 20 N m, so the 20 N force must act at 20 ÷ 20 = 1.0 m from the pivot.

Question 5Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A car moving at 4 m/s accelerates steadily at 3 m/s² for 5 s. What is its final speed?

  1. 19 m/s Correct answer.
  2. 15 m/s
  3. 35 m/s
  4. 7 m/s

Explanation

The final speed is found from v = u + at, where u is the initial speed, a the acceleration and t the time. Substituting gives 4 + (3 × 5) = 19 m/s. The acceleration adds 3 m/s to the speed every second for five seconds.

Question 6Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A car of mass 800 kg travels at 10 m/s. What is its kinetic energy?

  1. 80 000 J
  2. 40 000 J Correct answer.
  3. 160 000 J
  4. 4 000 J

Explanation

Kinetic energy is given by half the mass multiplied by the square of the speed. Here 0.5 × 800 × 10² = 40 000 J. Squaring the speed is essential because the energy depends on the square of the velocity, not on the velocity itself.

Question 7Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A worker lifts a load weighing 200 N through a vertical height of 3 m in 5 s at a steady speed. What useful power does the worker develop?

  1. 120 W Correct answer.
  2. 40 W
  3. 3000 W
  4. 600 W

Explanation

Power is the work done divided by the time taken. Lifting 200 N through 3 m requires 600 J of work, and 600 J ÷ 5 s gives 120 W. Power measures the rate of transferring energy, so the time must appear in the calculation.

Question 8Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A resultant force of 3600 N acts on a car of mass 1200 kg. What is the acceleration of the car?

  1. 30 m/s²
  2. 0.33 m/s²
  3. 4320 m/s²
  4. 3 m/s² Correct answer.

Explanation

Newton's second law links resultant force, mass and acceleration through F = ma. Rearranging gives a = F ÷ m = 3600 ÷ 1200 = 3 m/s². The acceleration is in the same direction as the resultant force acting on the car.

Question 9Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A student of mass 60 kg stands on bathroom scales inside a lift that is accelerating downwards at 2 m/s². Taking g as 10 N/kg, what reading do the scales show?

  1. 480 N Correct answer.
  2. 600 N
  3. 720 N
  4. 120 N

Explanation

The scales read the normal force from the floor, found from Newton's second law using the resultant force towards the centre of the motion. Taking downwards as positive, mg − R = ma, so R = m(g − a) = 60 × (10 − 2) = 480 N. The reading is below the true weight because the floor accelerates away from the student.

Question 10Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A pulley system has a velocity ratio of 5 and an efficiency of 60%. What effort is needed to raise a load of 300 N at a steady speed?

  1. 100 N Correct answer.
  2. 20 N
  3. 60 N
  4. 180 N

Explanation

Efficiency equals mechanical advantage divided by velocity ratio, so the mechanical advantage here is 0.60 × 5 = 3. Mechanical advantage is also load divided by effort, so the effort is 300 N ÷ 3 = 100 N. Friction in the pulley reduces the advantage below the velocity ratio.

Question 11Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

On a velocity–time graph, what does the gradient of the line represent?

  1. The displacement of the object
  2. The resultant force on the object
  3. The acceleration of the object Correct answer.
  4. The distance travelled by the object

Explanation

The gradient of a velocity–time graph is the change in velocity divided by the time taken, which is exactly the definition of acceleration. A horizontal line therefore represents zero acceleration, while a line sloping down towards the time axis represents deceleration.

Question 12Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A puck slides across a horizontal sheet of ice at a steady velocity. Friction and air resistance are negligible. What is the resultant force acting on the puck?

  1. A steady force in the direction of motion
  2. A force equal to the weight of the puck
  3. Zero Correct answer.
  4. A small force opposing the motion

Explanation

Newton's first law states that an object keeps a constant velocity only when the resultant force on it is zero. Moving at a steady speed in a straight line therefore requires no net force, and the weight is already cancelled by the upward normal reaction from the ice.

Question 13Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

An astronaut takes a tool of mass 2 kg from the Earth to the Moon, where the gravitational field strength is about one sixth of that on Earth. Which statement about the tool is correct?

  1. The mass is smaller and the weight is unchanged.
  2. The mass is 2 kg and the weight is smaller. Correct answer.
  3. The mass is smaller and the weight is smaller.
  4. The mass is unchanged and the weight is unchanged.

Explanation

Mass measures the amount of matter in an object and does not depend on location, so the tool is still 2 kg on the Moon. Weight is the product of mass and gravitational field strength, and since the Moon's field strength is weaker, the weight is smaller there.

Question 14Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A car travelling at 20 m/s brakes and comes to rest in a distance of 50 m. The braking force is constant. What is the magnitude of the deceleration?

  1. 5.0 m/s²
  2. 2.0 m/s²
  3. 4.0 m/s² Correct answer.
  4. 8.0 m/s²

Explanation

Using v² = u² + 2as with final speed zero, initial speed 20 m/s and distance 50 m gives 0 = 400 + 100a, so a = −4 m/s². The deceleration is the magnitude of this value, namely 4.0 m/s².

Question 15Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A spring obeys Hooke's law. A force of 6 N stretches it by 0.12 m. What force is needed to stretch the same spring by 0.20 m?

  1. 10 N Correct answer.
  2. 9 N
  3. 12 N
  4. 8 N

Explanation

Hooke's law gives F = kx, so the spring constant is 6 N ÷ 0.12 m = 50 N/m. Because extension is proportional to the applied force, the force needed for 0.20 m is 50 N/m × 0.20 m = 10 N.

Question 16Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A car travels at a constant speed of 15 m/s along a level road while its engine supplies a useful power of 30 kW. What is the total resistive force acting on the car?

  1. 200 N
  2. 2000 N Correct answer.
  3. 45 000 N
  4. 20 000 N

Explanation

Power is the rate of doing work, so P = Fv, where F is the driving force. Rearranging gives F = P ÷ v = 30 000 W ÷ 15 m/s = 2000 N, and at constant speed this driving force is equal in size to the total resistive force.

Question 17Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A crate weighing 300 N is pushed up a ramp 2.5 m long onto a platform 1.0 m high. The pushing force needed along the ramp is 150 N. What is the efficiency of the ramp?

  1. 67%
  2. 80% Correct answer.
  3. 75%
  4. 60%

Explanation

The useful work done is the gain in potential energy, 300 N × 1.0 m = 300 J. The work put in is the force along the ramp times the ramp length, 150 N × 2.5 m = 375 J, so efficiency = 300 ÷ 375 × 100% = 80%.

Question 18Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A ball is released from rest at a height of 1.8 m above the ground. Taking g as 10 m/s² and ignoring air resistance, what is the speed of the ball just before it hits the ground?

  1. 3.6 m/s
  2. 6.0 m/s Correct answer.
  3. 18 m/s
  4. 36 m/s

Explanation

With air resistance ignored, the gravitational potential energy lost equals the kinetic energy gained, so mgh = ½mv². Cancelling the mass gives v = √(2gh) = √(2 × 10 × 1.8) = √36 = 6.0 m/s, a result that does not depend on the mass of the ball.

Question 19Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A car travelling at 20 m/s stops in 40 m when its brakes are applied. The same car is then driven at 30 m/s and the same braking force is used. What is the stopping distance?

  1. 90 m Correct answer.
  2. 120 m
  3. 80 m
  4. 60 m

Explanation

The braking force does work Fd equal to the kinetic energy removed, ½mv², so the stopping distance is proportional to the square of the initial speed. Increasing the speed from 20 m/s to 30 m/s multiplies the distance by (1.5)² = 2.25, giving 40 m × 2.25 = 90 m.

Question 20Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A skydiver falls from rest and the air resistance on her increases as her speed increases, until the air resistance is equal to her weight. Which statement describes her motion at the moment this balance is reached?

  1. The acceleration is zero and the speed stays constant. Correct answer.
  2. The acceleration is downwards but smaller than g and the speed keeps rising.
  3. The acceleration is greatest and the speed keeps rising.
  4. The acceleration is zero and the speed begins to fall.

Explanation

When the upward air resistance equals the downward weight, the resultant force on the skydiver is zero. By Newton's second law there is then no acceleration, so she continues falling at a steady speed, which is called the terminal velocity.

Question 21Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

For an object moving in a straight line, a graph of distance travelled against time is plotted. What does the gradient of this graph represent?

  1. force
  2. acceleration
  3. speed Correct answer.
  4. displacement

Explanation

The gradient of a distance–time graph is the change in distance divided by the change in time. That ratio is the speed of the object.

Question 22Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

Which unit is used to measure energy in the SI system?

  1. joule Correct answer.
  2. pascal
  3. newton
  4. watt

Explanation

The joule is the SI unit of energy and work. One joule is the energy transferred when a force of one newton moves an object one metre.

Question 23Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A book rests on a table. The book pushes down on the table with a force equal to its weight. According to Newton's third law, which force is the paired reaction to this push?

  1. The table pushes up on the book with an equal force. Correct answer.
  2. The Earth pulls the book down with its weight.
  3. The book pulls the Earth upward with an equal force.
  4. The table pushes down on the floor with an equal force.

Explanation

Newton’s third law says that if A pushes B, then B pushes A with an equal and opposite force. The book pushes the table downward, so the table pushes the book upward.

Question 24Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A cyclist travelling at 5 m/s speeds up to 13 m/s in 4.0 s. What is the average acceleration?

  1. 8.0 m/s²
  2. 4.5 m/s²
  3. 2.0 m/s² Correct answer.
  4. 3.25 m/s²

Explanation

Average acceleration is the change in velocity divided by the time taken. The velocity increases by 8 m/s in 4.0 s, giving 2.0 m/s².

Question 25Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A car doubles its speed while its mass stays the same. By what factor does its kinetic energy change?

  1. It stays the same.
  2. It doubles.
  3. It becomes four times larger. Correct answer.
  4. It becomes eight times larger.

Explanation

Kinetic energy depends on the square of speed, since Ek = ½mv². Doubling v makes v² four times larger, so the kinetic energy becomes four times larger.

Question 26Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A wheelbarrow is loaded so that its centre of gravity is 0.60 m from the wheel axle. The handles are 1.20 m from the wheel axle. The load weighs 500 N. What upward effort at the handles is needed to hold the wheelbarrow steady?

  1. 1000 N
  2. 250 N Correct answer.
  3. 100 N
  4. 500 N

Explanation

For a wheelbarrow the wheel axle acts as the pivot. The load moment is 500 N × 0.60 m = 300 N m, so the effort moment must also be 300 N m. Dividing by the 1.20 m effort arm gives 250 N.

Question 27Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A pump lifts 150 kg of water through a vertical height of 6.0 m in 30 s. Taking g as 10 N/kg, what is the useful output power of the pump?

  1. 90 W
  2. 30 W
  3. 300 W Correct answer.
  4. 9000 W

Explanation

Useful work done is weight × height = (150 kg × 10 N/kg) × 6.0 m = 9000 J. Power is work done per second, so 9000 J ÷ 30 s = 300 W.

Question 28Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A lever has an effort arm of 0.80 m and a load arm of 0.20 m. Its efficiency is 75%. What effort is needed to raise a load of 900 N at a steady speed?

  1. 300 N Correct answer.
  2. 169 N
  3. 675 N
  4. 225 N

Explanation

The velocity ratio is 0.80 ÷ 0.20 = 4. Efficiency = (load ÷ effort) ÷ velocity ratio, so load ÷ effort = 0.75 × 4 = 3. The effort is therefore 900 N ÷ 3 = 300 N.

Question 29Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A 2.0 kg block starts from rest at the top of a slope 5.0 m high. As it slides down, 20 J of energy is transferred to thermal energy by friction. Taking g as 10 N/kg, what is the speed of the block at the bottom?

  1. 4.0 m/s
  2. 10 m/s
  3. 6.3 m/s
  4. 8.9 m/s Correct answer.

Explanation

Initial gravitational potential energy is mgh = 2.0 × 10 × 5.0 = 100 J. Subtracting 20 J lost to friction leaves 80 J of kinetic energy, and v = √(2 × 80 ÷ 2.0) = 8.9 m/s.

Question 30Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A car starts from rest and accelerates uniformly to 20 m/s in 8.0 s. It then travels at a constant 20 m/s for 12 s. Finally it decelerates uniformly to rest in 5.0 s. What is the total distance travelled?

  1. 280 m
  2. 370 m Correct answer.
  3. 520 m
  4. 400 m

Explanation

For each stage, distance is average velocity × time. The three distances are 10 × 8 = 80 m, 20 × 12 = 240 m, and 10 × 5 = 50 m, giving 370 m in total.

Question 31Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

Which of the following is a vector quantity?

  1. Mass
  2. Energy
  3. Force Correct answer.
  4. Speed

Explanation

A vector quantity has both size and direction, and a force is a push or pull that acts in a particular direction. Mass, speed and energy are scalars because each is fully described by its magnitude alone.

Question 32Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A cyclist travels a distance of 150 m in 25 s. What is the average speed of the cyclist?

  1. 175 m/s
  2. 0.17 m/s
  3. 6 m/s Correct answer.
  4. 3750 m/s

Explanation

Average speed is the total distance divided by the total time taken. Here 150 m ÷ 25 s = 6 m/s, so the cyclist covers 6 m each second on average.

Question 33Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A horizontal force of 40 N moves a box 3.0 m along the floor in the direction of the force. How much work is done by the force?

  1. 43 J
  2. 13.3 J
  3. 0 J
  4. 120 J Correct answer.

Explanation

Work done by a constant force is force multiplied by the distance moved along the force. The box moves 3.0 m in the direction of the 40 N force, so W = 40 × 3.0 = 120 J.

Question 34Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A 5.0 kg box on a horizontal floor is pulled by a horizontal force of 30 N. A friction force of 10 N acts on the box. What is the acceleration of the box?

  1. 8 m/s²
  2. 4 m/s² Correct answer.
  3. 2 m/s²
  4. 6 m/s²

Explanation

Newton's second law uses the resultant force, not just the applied force. The resultant force is 30 N − 10 N = 20 N, so a = F/m = 20/5.0 = 4 m/s².

Question 35Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A stone is thrown vertically upwards with a speed of 20 m/s. Taking g as 10 m/s², how long does the stone take to reach its highest point?

  1. 1 s
  2. 4 s
  3. 2 s Correct answer.
  4. 0.5 s

Explanation

At the highest point the upward velocity has fallen to zero. Using v = u + at with a = −10 m/s² gives 0 = 20 − 10t, so t = 2 s.

Question 36Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A uniform metre rule is balanced at its centre, the 50 cm mark. A 2 N weight is hung at the 20 cm mark. At which mark must a 4 N weight be hung to balance the rule?

  1. 70 cm
  2. 60 cm
  3. 80 cm
  4. 65 cm Correct answer.

Explanation

For balance, the clockwise moment about the pivot must equal the anticlockwise moment. The 2 N weight gives 2 × 30 = 60 N cm, so the 4 N weight needs a lever arm of 60/4 = 15 cm on the other side, at the 65 cm mark.

Question 37Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A pulley system has a velocity ratio of 5 and an efficiency of 80%. What effort is needed to raise a load of 400 N at a steady speed?

  1. 125 N
  2. 100 N Correct answer.
  3. 160 N
  4. 80 N

Explanation

Efficiency compares useful work output with work input, and for a pulley system efficiency = load ÷ (effort × velocity ratio). Rearranging gives effort = 400 ÷ (0.80 × 5) = 100 N.

Question 38Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A car of mass 800 kg accelerates from 10 m/s to 20 m/s. What is the work done by the resultant force on the car?

  1. 240 kJ
  2. 40 kJ
  3. 80 kJ
  4. 120 kJ Correct answer.

Explanation

The work done by the resultant force equals the change in kinetic energy. Change = ½ × 800 × (20² − 10²) = 400 × 300 = 120,000 J = 120 kJ.

Question 39Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A 60 kg crate is pulled up a 5.0 m long incline to a vertical height of 2.0 m at constant speed. The friction force on the crate is 50 N. Taking g as 10 N/kg, what is the pulling force parallel to the incline?

  1. 350 N
  2. 290 N Correct answer.
  3. 250 N
  4. 240 N

Explanation

The weight component acting down the slope is mg sinθ = 600 × (2.0/5.0) = 240 N. At constant speed the applied force must also overcome the 50 N friction, so it is 240 + 50 = 290 N.

Question 40Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

An electric motor lifts a 50 kg load at a constant speed of 2.0 m/s. The efficiency of the motor is 80%. Taking g as 10 N/kg, what is the electrical power input to the motor?

  1. 1000 W
  2. 1250 W Correct answer.
  3. 1600 W
  4. 800 W

Explanation

Useful power is force × speed, where the force equals the load's weight: 500 N × 2.0 m/s = 1000 W. Since efficiency = useful power ÷ input power, input = 1000 ÷ 0.80 = 1250 W.

Question 41Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

The area under a velocity-time graph represents which quantity?

  1. Force
  2. Speed
  3. Displacement Correct answer.
  4. Acceleration

Explanation

The area under a velocity-time graph is found by multiplying velocity by time, which gives displacement. Acceleration is represented by the gradient of the graph, not its area. Speed is the magnitude of velocity, and force is unrelated to this area.

Question 42Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A passenger standing in a bus is thrown forward when the bus brakes suddenly. Which property of the passenger explains this?

  1. Weight
  2. Inertia Correct answer.
  3. Friction
  4. Momentum

Explanation

Inertia is the tendency of an object to resist changes in its motion. When the bus brakes, the passenger's body continues moving forward at the original speed. Momentum and weight are quantities, while friction acts between surfaces, so none of these directly names this property.

Question 43Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

An object has a mass of 2.0 kg. Taking the gravitational field strength as 10 N/kg, what is its weight?

  1. 10 N
  2. 0.2 N
  3. 20 N Correct answer.
  4. 2 N

Explanation

Weight is calculated using the equation weight = mass × gravitational field strength. Substituting the values gives 2.0 kg × 10 N/kg = 20 N. The mass itself is 2.0 kg, not a force.

Question 44Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A stone is dropped from rest from a height of 45 m. Taking g as 10 m/s², how long does it take to reach the ground?

  1. 1.5 s
  2. 2.0 s
  3. 4.5 s
  4. 3.0 s Correct answer.

Explanation

Using the equation s = ut + ½at² with u = 0, s = 45 m and a = 10 m/s² gives 45 = 5t². Solving gives t² = 9, so t = 3.0 s. The other values do not satisfy this equation.

Question 45Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A 2.0 kg trolley moving at 3.0 m/s collides with a stationary 1.0 kg trolley. They stick together. What is their common velocity after the collision?

  1. 1.5 m/s
  2. 2.0 m/s Correct answer.
  3. 3.0 m/s
  4. 1.0 m/s

Explanation

Momentum is conserved in the collision. Total momentum before is 2.0 kg × 3.0 m/s = 6.0 kg m/s, and total mass after is 3.0 kg. Dividing gives a common velocity of 2.0 m/s.

Question 46Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A resultant force of 12 N acts on a 4.0 kg object. What is the acceleration of the object?

  1. 8.0 m/s²
  2. 3.0 m/s² Correct answer.
  3. 0.33 m/s²
  4. 48 m/s²

Explanation

Newton's second law gives the relationship force = mass × acceleration. Rearranging gives acceleration = force ÷ mass = 12 N ÷ 4.0 kg = 3.0 m/s². The other values come from adding, subtracting or multiplying the given numbers incorrectly.

Question 47Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A force of 20 N is applied to a spanner at a perpendicular distance of 0.15 m from the nut. What is the moment of the force about the nut?

  1. 0.75 N m
  2. 300 N m
  3. 3.0 N m Correct answer.
  4. 1.5 N m

Explanation

The moment of a force is calculated as force × perpendicular distance from the pivot. Multiplying 20 N by 0.15 m gives 3.0 N m. The distance must be measured perpendicular to the line of action of the force.

Question 48Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A 0.50 kg ball is lifted from the floor to a shelf 2.0 m high. Taking g as 10 N/kg, what is the gain in gravitational potential energy?

  1. 5.0 J
  2. 10 J Correct answer.
  3. 20 J
  4. 1.0 J

Explanation

Gravitational potential energy gained is calculated as mass × g × height. Substituting gives 0.50 kg × 10 N/kg × 2.0 m = 10 J. The height and mass must both be included in the multiplication.

Question 49Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A ball is thrown horizontally at 15 m/s from a cliff 20 m high. Taking g as 10 m/s², how far from the base of the cliff does the ball land?

  1. 15 m
  2. 30 m Correct answer.
  3. 20 m
  4. 60 m

Explanation

The vertical fall time is found from h = ½gt², so 20 = 5t² and t = 2.0 s. The horizontal distance is constant horizontal speed × time = 15 m/s × 2.0 s = 30 m. Horizontal and vertical motions are independent.

Question 50Mechanics: kinematics, dynamics, forces, moments, work, energy, power and machines

A wheel and axle has a wheel radius of 0.40 m and an axle radius of 0.10 m. Its efficiency is 80%. What effort is needed to lift a load of 160 N?

  1. 60 N
  2. 80 N
  3. 40 N
  4. 50 N Correct answer.

Explanation

The velocity ratio is wheel radius ÷ axle radius = 0.40 ÷ 0.10 = 4. Efficiency = (load × distance load moves) ÷ (effort × distance effort moves), so effort = load ÷ (velocity ratio × efficiency). Thus effort = 160 N ÷ (4 × 0.80) = 50 N.