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Question 1Mechanika
A car travels 150 m in 10 s at constant speed. What is its speed?
- 150 m/s
- 1,5 m/s
- 15 m/s Correct answer.
- 1500 m/s
Explanation
For constant speed, v = s/t. Substituting s = 150 m and t = 10 s gives v = 15 m/s.
Question 2Mechanika
Which quantity is a scalar?
- Acceleration
- Mass Correct answer.
- Velocity
- Displacement
Explanation
A scalar is fully described by magnitude alone, and mass has no direction. Velocity, acceleration and displacement all require a direction, so they are vectors.
Question 3Mechanika
A body moves with constant velocity. What is the net force acting on it?
- Increasing with time
- Constant but non-zero
- Zero Correct answer.
- Equal to its weight
Explanation
By Newton's first law, constant velocity means zero acceleration, and F = ma then requires the net force to be zero. The forces present must cancel.
Question 4Mechanika
What is the SI unit of work?
- Watt
- Joule Correct answer.
- Pascal
- Newton
Explanation
Work is force times displacement along the force, so its unit is the newton-metre, called the joule. The joule is the SI unit of energy and work.
Question 5Mechanika
A stone is dropped from rest and falls freely for 2 s. Taking g = 10 m/s², how far does it fall?
- 40 m
- 5 m
- 10 m
- 20 m Correct answer.
Explanation
For free fall from rest, s = ½gt². With g = 10 m/s² and t = 2 s, s = ½ · 10 · 4 = 20 m.
Question 6Mechanika
Which of these is a unit of power?
- kg·m/s
- J/s Correct answer.
- J·s
- N·m
Explanation
Power is the rate of doing work, so it is energy divided by time, measured in joules per second (the watt).
Question 7Mechanika
A body of mass 4 kg is acted on by a net force of 12 N. What is its acceleration?
- 48 m/s²
- 8 m/s²
- 0,33 m/s²
- 3 m/s² Correct answer.
Explanation
Newton's second law gives a = F/m. Substituting F = 12 N and m = 4 kg gives a = 3 m/s².
Question 8Mechanika
Two forces of 3 N and 4 N act at right angles on a point. What is the magnitude of their resultant?
- 1 N
- 7 N
- 12 N
- 5 N Correct answer.
Explanation
Perpendicular forces add as vectors, so the resultant magnitude is √(3² + 4²) = √25 = 5 N. This is the Pythagorean relation for perpendicular components.
Question 9Mechanika
A block slides at constant speed down a rough incline. Which statement about the forces is correct?
- The net force points down the incline
- The normal force equals the weight
- The friction force equals the component of weight along the incline Correct answer.
- Friction is greater than the driving component of weight
Explanation
Constant velocity means zero net force along the incline, so friction must exactly balance the downhill component of weight. The normal force balances only the perpendicular component of weight.
Question 10Mechanika
A ball is thrown vertically upward with 20 m/s. Taking g = 10 m/s² and ignoring air resistance, how long does it take to reach its highest point?
- 1 s
- 0,5 s
- 4 s
- 2 s Correct answer.
Explanation
At the highest point the velocity is zero, so from v = v₀ − gt we get t = v₀/g = 20/10 = 2 s.
Question 11Mechanika
A 2 kg object moving at 3 m/s collides head-on with a stationary 4 kg object and they stick together. What is their common velocity after the collision?
- 1 m/s Correct answer.
- 0,5 m/s
- 2 m/s
- 1,5 m/s
Explanation
Momentum is conserved in the collision: 2·3 + 4·0 = (2 + 4)·v. Solving gives v = 6/6 = 1 m/s.
Question 12Mechanika
A force of 50 N pushes a crate 4 m along the direction of motion. What work is done?
- 400 J
- 12,5 J
- 200 J Correct answer.
- 54 J
Explanation
Work equals force times displacement when they are parallel: W = F·s = 50 · 4 = 200 J.
Question 13Mechanika
A 2 kg ball is lifted to a height of 5 m. Taking g = 10 m/s², what is its gain in gravitational potential energy?
- 100 J Correct answer.
- 50 J
- 10 J
- 20 J
Explanation
Gravitational potential energy gain is mgh. Substituting 2 · 10 · 5 gives 100 J.
Question 14Mechanika
A machine lifts a 200 N load 3 m in 6 s. What is its average output power?
- 3600 W
- 100 W Correct answer.
- 50 W
- 600 W
Explanation
Work done is F·s = 200 · 3 = 600 J, and power is work over time: 600/6 = 100 W.
Question 15Mechanika
Two satellites orbit Earth at different radii. Which statement about their motion is correct?
- The satellite at the larger radius has the greater speed
- Speed depends only on the satellite mass
- The satellite at the larger radius has the smaller speed Correct answer.
- Both satellites have the same speed because gravity is the same
Explanation
For a circular orbit, gravity provides the centripetal force: GMm/r² = mv²/r, so v = √(GM/r). Speed therefore decreases as orbital radius increases.
Question 16Mechanika
A wheel rotates at a constant 30 revolutions per minute. What is its angular speed in radians per second?
- 60π rad/s
- 30 rad/s
- π rad/s Correct answer.
- 0,5 rad/s
Explanation
One revolution is 2π radians and one minute is 60 s, so ω = 30 · 2π / 60 = π rad/s.
Question 17Mechanika
A body moves in a circle at constant speed. Which statement is correct?
- Its acceleration points toward the centre of the circle Correct answer.
- Its acceleration is zero because the speed is constant
- Its velocity is constant
- Its acceleration points along the direction of motion
Explanation
In uniform circular motion the speed is constant but the direction of velocity changes, producing a centripetal acceleration directed toward the centre.
Question 18Mechanika
A spring obeys Hooke's law with a spring constant of 200 N/m. How much force is needed to stretch it by 5 cm?
- 10 N Correct answer.
- 4 N
- 1000 N
- 40 N
Explanation
Hooke's law gives F = k·x. Converting 5 cm to 0,05 m, F = 200 · 0,05 = 10 N.
Question 19Mechanika
An object of mass 5 kg is at rest. A constant net force of 10 N acts on it for 3 s. What is its final momentum?
- 50 kg·m/s
- 6 kg·m/s
- 150 kg·m/s
- 30 kg·m/s Correct answer.
Explanation
The impulse equals the change in momentum: F·t = 10 · 3 = 30 kg·m/s. Starting from rest, this is the final momentum.
Question 20Mechanika
A 60 kg person stands in a lift that accelerates upward at 2 m/s². Taking g = 10 m/s², what is the normal force from the floor?
- 600 N
- 480 N
- 720 N Correct answer.
- 120 N
Explanation
The net force upward is N − mg = ma, so N = m(g + a) = 60 · 12 = 720 N. The floor must also supply the force needed to accelerate the person.
Question 21Mechanika
A 4 kg block moving at 5 m/s slides on a rough surface and stops after 10 m. What is the magnitude of the friction force?
- 10 N
- 2 N
- 20 N
- 5 N Correct answer.
Explanation
The kinetic energy ½mv² = ½ · 4 · 25 = 50 J is dissipated by friction over 10 m. Thus F = W/s = 50/10 = 5 N.
Question 22Mechanika
A projectile is launched at 20 m/s at 30° above the horizontal. Taking g = 10 m/s² and ignoring air resistance, what is its maximum height?
- 20 m
- 10 m
- 5 m Correct answer.
- 15 m
Explanation
The vertical component is v₀ sin30° = 10 m/s. The maximum height is v_y²/(2g) = 100/20 = 5 m.
Question 23Mechanika
A 3 kg object moving at 4 m/s collides elastically head-on with a 1 kg object at rest. What is the velocity of the 3 kg object after the collision?
- 2 m/s Correct answer.
- 0 m/s
- 4 m/s
- −2 m/s
Explanation
For an elastic collision with a stationary target, v₁' = (m₁ − m₂)/(m₁ + m₂) · v₁ = (2/4)·4 = 2 m/s. Both momentum and kinetic energy are conserved.
Question 24Mechanika
A block of mass m slides from rest down a frictionless incline of height h and then compresses a spring at the bottom. Which relation gives the maximum compression x if the spring constant is k?
- x = mgh/k
- x = √(2mgh/k) Correct answer.
- x = 2mgh/k
- x = √(mgh/k)
Explanation
Energy conservation gives mgh = ½kx², so x = √(2mgh/k). The potential energy lost by the block becomes elastic energy in the spring.
Question 25Mechanika
A body of mass 2 kg moves in a circle of radius 0,5 m at a constant speed of 4 m/s. What is the centripetal force?
- 32 N
- 8 N
- 64 N Correct answer.
- 16 N
Explanation
The centripetal force is F = mv²/r = 2 · 16 / 0,5 = 64 N. It is directed toward the centre of the circle.
Question 26Mechanika
Which of the following is a vector quantity?
- Velocity Correct answer.
- Time
- Mass
- Speed
Explanation
A vector has both magnitude and direction. Velocity includes direction, while speed, mass, and time are scalars.
Question 27Mechanika
A car travels 100 m in 5 s. What is its average speed?
- 10 m/s
- 25 m/s
- 20 m/s Correct answer.
- 5 m/s
Explanation
Average speed is distance divided by time: 100 m / 5 s = 20 m/s.
Question 28Mechanika
A body starts from rest and accelerates uniformly at 2 m/s². How far does it travel in 3 s?
- 6 m
- 9 m Correct answer.
- 12 m
- 18 m
Explanation
Using s = ut + ½at² with u = 0, s = ½ × 2 × 3² = 9 m.
Question 29Mechanika
According to Newton's third law, when a hammer exerts a force on a nail, the nail exerts on the hammer:
- A smaller force in the same direction
- A larger force in the opposite direction
- A force of equal magnitude in the opposite direction Correct answer.
- No force because the nail is at rest
Explanation
Newton's third law states that forces come in pairs of equal magnitude and opposite direction, acting on different bodies.
Question 30Mechanika
A force of 10 N acts at 30° above the horizontal. What is the horizontal component of the force?
- 5.0 N
- 10 N
- 8.7 N Correct answer.
- 0 N
Explanation
The horizontal component is F cos θ = 10 × cos 30° ≈ 8.7 N.
Question 31Mechanika
A block of mass 2 kg is pulled along a horizontal surface by a horizontal force of 10 N. The coefficient of kinetic friction is 0.2. Taking g = 10 m/s², what is the acceleration of the block?
- 2 m/s²
- 1 m/s²
- 5 m/s²
- 3 m/s² Correct answer.
Explanation
Friction force f = μmg = 0.2 × 2 × 10 = 4 N. Net force = 10 − 4 = 6 N, so a = F_net/m = 6/2 = 3 m/s².
Question 32Mechanika
A ball is dropped from rest from a height of 20 m. Taking g = 10 m/s² and ignoring air resistance, what is its speed just before hitting the ground?
- 10 m/s
- 20 m/s Correct answer.
- 40 m/s
- 30 m/s
Explanation
Using v² = u² + 2as with u = 0, v = √(2 × 10 × 20) = √400 = 20 m/s.
Question 33Mechanika
A 0.5 kg ball moving at 4 m/s collides with a wall and rebounds with a speed of 3 m/s in the opposite direction. What is the magnitude of the impulse exerted by the wall on the ball?
- 7.0 N·s
- 0.5 N·s
- 2.0 N·s
- 3.5 N·s Correct answer.
Explanation
Impulse equals change in momentum: Δp = m(v_f − v_i). Taking the initial direction as positive, v_i = 4 m/s and v_f = −3 m/s, so Δp = 0.5 × (−3 − 4) = −3.5 N·s. The magnitude is 3.5 N·s.
Question 34Mechanika
A machine does 600 J of work in 2 minutes. What is its average power output?
- 10 W
- 1200 W
- 300 W
- 5 W Correct answer.
Explanation
Power is work divided by time: P = 600 J / 120 s = 5 W.
Question 35Mechanika
A 2 kg object moving at 6 m/s collides head-on with a 4 kg object moving at 3 m/s in the opposite direction. They stick together. What is the velocity of the combined mass?
- 1 m/s in the direction of the 2 kg object
- 1 m/s in the direction of the 4 kg object
- 0 m/s Correct answer.
- 2 m/s in the direction of the 2 kg object
Explanation
Total momentum before = (2 × 6) + (4 × (−3)) = 12 − 12 = 0. After sticking, momentum is conserved, so the combined velocity is 0 m/s.
Question 36Mechanika
A 0.2 kg stone is whirled in a horizontal circle of radius 0.5 m at a constant speed of 4 m/s. What is the tension in the string?
- 6.4 N Correct answer.
- 3.2 N
- 0.8 N
- 1.6 N
Explanation
The centripetal force is provided by the tension: T = mv²/r = 0.2 × 4² / 0.5 = 0.2 × 16 / 0.5 = 6.4 N.
Question 37Mechanika
A 1 kg object moving at 2 m/s collides elastically head-on with a 3 kg object at rest. What is the velocity of the 1 kg object after the collision?
- 1 m/s
- −1 m/s Correct answer.
- −2 m/s
- 2 m/s
Explanation
For an elastic collision with a stationary target, v1' = (m1 − m2)/(m1 + m2) × u1 = (1 − 3)/(1 + 3) × 2 = (−2/4) × 2 = −1 m/s. The negative sign indicates rebound.
Question 38Mechanika
A block of mass m is released from rest at the top of a frictionless incline of height h and compresses a spring of spring constant k at the bottom. What is the maximum compression x of the spring?
- x = √(mgh/k)
- x = √(2mgh/k) Correct answer.
- x = mgh/k
- x = 2mgh/k
Explanation
Gravitational potential energy mgh is converted into elastic potential energy ½kx². Equating gives ½kx² = mgh, so x = √(2mgh/k).
Question 39Mechanika
A 60 kg person stands on a scale in a lift. The scale reads 720 N. Taking g = 10 m/s², what is the acceleration of the lift?
- 12 m/s² upward
- 0 m/s²
- 2 m/s² upward Correct answer.
- 2 m/s² downward
Explanation
The normal force N = m(g + a). Here 720 = 60(10 + a), so 10 + a = 12, giving a = 2 m/s² upward.
Question 40Mechanika
A body moves in a circle at constant speed. Which statement about its acceleration is correct?
- It is directed away from the center.
- It is zero because the speed is constant.
- It is directed toward the center and has constant magnitude. Correct answer.
- It is directed tangent to the circle.
Explanation
In uniform circular motion, the acceleration is centripetal: it points toward the center and has magnitude v²/r, which is constant if v and r are constant.
Question 41Termodynamika a molekulová fyzika
What is the SI unit of thermodynamic temperature?
- Celsius
- Joule
- Fahrenheit
- Kelvin Correct answer.
Explanation
Thermodynamic temperature is a base quantity in the SI system and its unit is the kelvin. Celsius and Fahrenheit are practical temperature scales, and the joule is a unit of energy.
Question 42Termodynamika a molekulová fyzika
Which quantity is a state function of a thermodynamic system?
- Heat
- Path length of the process
- Internal energy Correct answer.
- Work
Explanation
A state function depends only on the current state of the system, not on how that state was reached. Internal energy is such a quantity, while work and heat depend on the path taken.
Question 43Termodynamika a molekulová fyzika
The first law of thermodynamics for a system that exchanges only heat and volume work can be written as:
- ΔU = 0 always
- ΔU = Q + W with W the work done by the system
- ΔU = W − Q
- ΔU = Q − W Correct answer.
Explanation
The change in internal energy equals the heat added to the system minus the work done by the system. This is the standard sign convention where Q is heat supplied and W is work performed by the gas.
Question 44Termodynamika a molekulová fyzika
An ideal gas is enclosed in a rigid container. During heating, which quantity is zero?
- Change of temperature
- Work done by the gas Correct answer.
- Change of internal energy
- Heat supplied
Explanation
In a rigid container the volume cannot change, so the gas performs no volume work. Heat supplied goes entirely into raising the internal energy and temperature.
Question 45Termodynamika a molekulová fyzika
What is the approximate value of the molar gas constant R?
- 6.02 × 10²³ mol⁻¹
- 9.81 m·s⁻²
- 8.31 J·mol⁻¹·K⁻¹ Correct answer.
- 1.38 × 10⁻²³ J·K⁻¹
Explanation
The molar gas constant relates pressure, volume and temperature in the ideal gas law and equals about 8.31 J·mol⁻¹·K⁻¹. The other values are the Boltzmann constant, the Avogadro constant and gravitational acceleration.
Question 46Termodynamika a molekulová fyzika
In an ideal gas, the average kinetic energy of translation of one molecule depends only on:
- Pressure
- Molar mass
- Absolute temperature Correct answer.
- Volume
Explanation
The kinetic theory gives average translational kinetic energy (3/2)kT, which depends only on absolute temperature. Pressure and volume affect the gas collectively but not the mean kinetic energy per molecule at a given temperature.
Question 47Termodynamika a molekulová fyzika
Which process is described as adiabatic?
- A process at constant temperature
- A process at constant volume
- A process with no heat exchange with the surroundings Correct answer.
- A process at constant pressure
Explanation
An adiabatic process is one in which no heat is exchanged with the surroundings, so Q = 0. Constant pressure, temperature and volume define isobaric, isothermal and isochoric processes respectively.
Question 48Termodynamika a molekulová fyzika
Which statement about the second law of thermodynamics is correct?
- Heat can never flow from a colder body to a hotter body under any circumstances
- All reversible engines have efficiency equal to one
- The entropy of an isolated system always decreases
- Heat cannot spontaneously flow from a colder body to a hotter body without external work Correct answer.
Explanation
The second law forbids spontaneous heat flow from cold to hot, but a refrigerator can transfer heat that way when work is supplied. Entropy of an isolated system never decreases, and no engine reaches unit efficiency.
Question 49Termodynamika a molekulová fyzika
A gas at constant pressure of 2.0 × 10⁵ Pa expands from 0.010 m³ to 0.030 m³. How much work does the gas do?
- 6.0 × 10³ J
- 2.0 × 10³ J
- 4.0 × 10³ J Correct answer.
- 8.0 × 10³ J
Explanation
For an isobaric process the work done by the gas is W = p·ΔV. Here ΔV = 0.020 m³, so W = 2.0 × 10⁵ × 0.020 = 4.0 × 10³ J.
Question 50Termodynamika a molekulová fyzika
An ideal gas is compressed isothermally. What happens to its internal energy?
- It stays the same Correct answer.
- It decreases
- It increases
- It becomes zero
Explanation
For an ideal gas the internal energy depends only on temperature. In an isothermal process the temperature is constant, so the internal energy does not change.