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LC Physics practice questions

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Question 1Mechanics

A cyclist moves 3 km east and then 4 km north. Which quantity used to describe this journey is a vector?

  1. Displacement Correct answer.
  2. Distance travelled
  3. Time taken
  4. Average speed

Explanation

Displacement is a vector because it has both magnitude and direction; here it is 5 km on a bearing of about 053°. Distance, speed and time are scalars, possessing magnitude only. The distinction matters when adding motions that are not along the same line.

Question 2Mechanics

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

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

Explanation

By Newton's first law, a body continues in uniform motion unless acted on by a net external force. When the bus decelerates, the floor exerts little backward force on the passenger, so the passenger tends to keep moving forward. Inertia is the property of resisting change in motion.

Question 3Mechanics

In mechanics, the joule is the SI unit of which quantity?

  1. Force
  2. Power
  3. Work Correct answer.
  4. Momentum

Explanation

One joule is the work done when a force of one newton moves its point of application one metre in the direction of the force. Work and energy are therefore measured in joules. Force is measured in newtons, power in watts and momentum in kilogram metres per second.

Question 4Mechanics

A ball is projected horizontally at 4 m/s from the edge of a table. Ignoring air resistance, which statement about its motion is correct?

  1. The horizontal velocity remains constant while the vertical velocity increases at g. Correct answer.
  2. The horizontal velocity decreases while the vertical velocity increases.
  3. Both the horizontal and vertical motions have an acceleration of g.
  4. The time of flight depends on the horizontal velocity.

Explanation

With air resistance ignored, no horizontal force acts, so the horizontal component of velocity stays at 4 m/s. Vertically the ball starts from rest and accelerates downwards at g, so its vertical velocity increases uniformly. The time of flight is set by the vertical fall distance, not by the horizontal speed.

Question 5Mechanics

A 2 kg trolley moving at 3 m/s collides with a stationary 4 kg trolley. The trolleys stick together. What is their common velocity immediately after the collision?

  1. 1.5 m/s
  2. 2 m/s
  3. 1 m/s Correct answer.
  4. 0.5 m/s

Explanation

Total momentum before the collision is (2 kg)(3 m/s) = 6 kg m/s, and the stationary trolley contributes zero. After the collision the combined mass is 6 kg, so conservation of momentum gives 6 = 6v, hence v = 1 m/s. The collision is perfectly inelastic, so kinetic energy is not conserved.

Question 6Mechanics

A uniform metre stick is pivoted at its centre. A 2 N weight is hung 20 cm to the left of the pivot. At what distance to the right of the pivot must a 4 N weight be hung to balance the stick?

  1. 40 cm
  2. 5 cm
  3. 10 cm Correct answer.
  4. 20 cm

Explanation

By the principle of moments, the clockwise moment must equal the anticlockwise moment about the pivot. The left-hand moment is 2 N × 0.20 m = 0.40 N m, so the 4 N weight must be at 0.40 ÷ 4 = 0.10 m from the pivot. That is 10 cm to the right.

Question 7Mechanics

A car travels at constant speed around a circular track. Which statement about the car is correct?

  1. Its velocity is constant because the track is circular.
  2. It has an acceleration directed towards the centre of the circle. Correct answer.
  3. Its acceleration is zero because its speed is constant.
  4. The net force on it acts in the direction of its motion.

Explanation

Velocity is a vector, so a change in direction is a change in velocity even when speed is constant. The car therefore accelerates, and this centripetal acceleration points towards the centre of the circular path. The net force, friction in this case, must also point towards the centre.

Question 8Mechanics

A spring extends by 4 cm when a 2 N force is applied. Assuming Hooke's law applies, what force is needed to extend the same spring by 10 cm?

  1. 4 N
  2. 0.8 N
  3. 2.5 N
  4. 5 N Correct answer.

Explanation

Hooke's law states that extension is directly proportional to the applied force, F = kx. The spring constant is k = 2 N ÷ 0.04 m = 50 N/m. For an extension of 0.10 m the force is F = 50 × 0.10 = 5 N.

Question 9Mechanics

A satellite in a circular orbit of radius r around Earth has an orbital period T. It is moved to a circular orbit of radius 4r. What is its new orbital period?

  1. 4T
  2. 8T Correct answer.
  3. 16T
  4. 2T

Explanation

Kepler's third law for satellites of the same central body gives T² ∝ r³. If the radius increases by a factor of 4, then T² increases by 4³ = 64. Taking the square root, the period increases by a factor of 8.

Question 10Mechanics

Two masses, 3 kg and 1 kg, are connected by a light string over a frictionless pulley. What is the acceleration of the system when released?

  1. 9.8 m/s²
  2. 4.9 m/s² Correct answer.
  3. 2.45 m/s²
  4. 7.35 m/s²

Explanation

The net driving force is the difference in weights, (3 − 1)g = 2g, and the total mass being accelerated is 3 + 1 = 4 kg. Applying Newton's second law gives a = 2g/4 = g/2 ≈ 4.9 m/s². The 3 kg mass descends and the 1 kg mass rises with this acceleration.

Question 11Mechanics

A book rests on a horizontal table. Which pair of forces is an action-reaction pair according to Newton's third law?

  1. The normal force of the table on the book and the weight of the table
  2. Earth's pull on the book and the book's pull on Earth Correct answer.
  3. The weight of the book and the normal force of the table on the book
  4. The force of the book on the table and the weight of the book

Explanation

Newton's third law pairs are equal and opposite forces that act on two different bodies and arise from the same interaction. The gravitational interaction between Earth and the book gives one force on the book and an equal and opposite force on Earth. The weight and the normal force both act on the book, so they are a balanced pair rather than a third-law pair.

Question 12Mechanics

A metal block has a mass of 2.0 kg and a volume of 1.0 × 10^-3 m^3. What is its density?

  1. 5.0 × 10^-4 kg m^-3
  2. 2.0 × 10^3 kg m^-3 Correct answer.
  3. 2.0 × 10^-3 kg m^-3
  4. 5.0 × 10^2 kg m^-3

Explanation

Density is mass divided by volume, so the calculation is 2.0 kg ÷ 1.0 × 10^-3 m^3. Dividing by 10^-3 is the same as multiplying by 10^3, giving 2.0 × 10^3 kg m^-3.

Question 13Mechanics

Which expression gives the SI unit of momentum in base units?

  1. kg m^2 s^-2
  2. kg m s^-2
  3. kg m^2 s^-3
  4. kg m s^-1 Correct answer.

Explanation

Momentum is mass multiplied by velocity, so its unit is the kilogram multiplied by metres per second. This gives kg m s^-1 in SI base units. The other expressions correspond to force, energy, and power.

Question 14Mechanics

A car accelerates uniformly from rest to 20 m/s in 5.0 s. What distance does it travel during this time?

  1. 40 m
  2. 20 m
  3. 50 m Correct answer.
  4. 100 m

Explanation

For uniform acceleration, the average velocity is the mean of the initial and final velocities: (0 + 20)/2 = 10 m/s. The distance is average velocity multiplied by time, so 10 × 5.0 = 50 m.

Question 15Mechanics

A ball of mass 0.20 kg strikes a wall horizontally at 10 m/s and rebounds horizontally at 8.0 m/s. What is the magnitude of the impulse exerted by the wall on the ball?

  1. 0.40 N s
  2. 2.0 N s
  3. 3.6 N s Correct answer.
  4. 1.6 N s

Explanation

Impulse equals change in momentum. Taking the direction away from the wall as positive, the velocity changes from -10 m/s to +8.0 m/s, so the change is 18 m/s. The impulse is 0.20 × 18 = 3.6 N s.

Question 16Mechanics

A pump raises 200 kg of water through a vertical height of 10 m in 20 s. Taking g = 10 m/s^2, what is the useful output power of the pump?

  1. 20 000 W
  2. 2000 W
  3. 100 W
  4. 1000 W Correct answer.

Explanation

The useful work done is the gain in gravitational potential energy, mgh = 200 × 10 × 10 = 20 000 J. Power is work divided by time, so 20 000 J ÷ 20 s = 1000 W.

Question 17Mechanics

A car travels around a circular bend of radius 50 m at a constant speed of 20 m/s. What is the magnitude of its centripetal acceleration?

  1. 400 m/s^2
  2. 4.0 m/s^2
  3. 0.40 m/s^2
  4. 8.0 m/s^2 Correct answer.

Explanation

Centripetal acceleration has magnitude v^2/r. Substituting gives 20^2 ÷ 50 = 400 ÷ 50 = 8.0 m/s^2. The acceleration points toward the centre of the circular path.

Question 18Mechanics

A block of mass 5.0 kg rests on a horizontal surface. The coefficient of static friction between the block and the surface is 0.30. Taking g = 10 m/s^2, what is the maximum static friction force that can act on the block?

  1. 5.0 N
  2. 15 N Correct answer.
  3. 0.30 N
  4. 50 N

Explanation

The normal force on the horizontal surface is equal to the block's weight, mg = 5.0 × 10 = 50 N. The maximum static friction is μN = 0.30 × 50 = 15 N.

Question 19Mechanics

At the surface of Earth, the gravitational field strength is g. What is the gravitational field strength at a height above the surface equal to Earth's radius? Treat Earth as a uniform sphere.

  1. g/16
  2. g/9
  3. g/2
  4. g/4 Correct answer.

Explanation

The gravitational field strength is proportional to 1/r^2, where r is the distance from Earth's centre. At a height equal to Earth's radius, the distance from the centre is 2R, so the field is g × (R/2R)^2 = g/4.

Question 20Mechanics

A simple pendulum has period T. If its length is increased to four times its original value, and the amplitude remains small, what is the new period?

  1. T/4
  2. 2T Correct answer.
  3. T/2
  4. 4T

Explanation

For a simple pendulum with small amplitude, the period is T = 2π√(L/g), so the period is proportional to the square root of the length. Increasing the length by a factor of four multiplies the period by √4 = 2. The new period is therefore 2T.

Question 21Mechanics

A car's velocity-time graph is a straight line through the origin. Which quantity is represented by the gradient of this line?

  1. Power
  2. Displacement
  3. Acceleration Correct answer.
  4. Momentum

Explanation

On a velocity-time graph the gradient equals the rate of change of velocity, which is acceleration. A straight line through the origin means the acceleration is constant while the velocity increases from zero. The area under the line would instead give displacement.

Question 22Mechanics

A crate of weight 200 N is pushed across a horizontal floor at a constant speed by a horizontal force of 60 N. What is the magnitude of the friction force acting on the crate?

  1. 140 N
  2. 60 N Correct answer.
  3. 260 N
  4. 200 N

Explanation

Constant speed means the horizontal forces are balanced, so the friction force must equal the applied push. The vertical forces, weight and normal reaction, are also balanced but do not cancel the horizontal push. Therefore friction is 60 N, directed opposite to the motion.

Question 23Mechanics

A crane lifts a 500 kg load vertically at a constant speed of 2.0 m/s. Taking g = 10 m/s^2, what useful power does the crane develop?

  1. 10 kW Correct answer.
  2. 20 kW
  3. 2.5 kW
  4. 1.0 kW

Explanation

Useful power equals force times speed. The lifting force equals the load's weight, 500 × 10 = 5000 N, so power = 5000 × 2.0 = 10 000 W = 10 kW. Because the speed is constant, no extra resultant force is needed to accelerate the load.

Question 24Mechanics

A ball is thrown vertically upwards with an initial speed of 20 m/s. Taking g = 10 m/s^2 and ignoring air resistance, how long does it take to return to the thrower's hand?

  1. 4.0 s Correct answer.
  2. 2.0 s
  3. 40 s
  4. 20 s

Explanation

The time to reach the highest point is v/g = 20/10 = 2.0 s, because the vertical velocity decreases by 10 m/s each second. The upward and downward journeys take equal times when air resistance is ignored, so the total time is 4.0 s.

Question 25Mechanics

A block slides down a rough inclined plane at constant velocity. Which statement about the forces on the block is correct?

  1. Friction is greater than the weight component.
  2. Resultant force down the slope is non-zero.
  3. Weight component down slope equals friction. Correct answer.
  4. Normal reaction equals the block's weight.

Explanation

Constant velocity means zero resultant force along the slope. Therefore the component of weight acting down the slope must be exactly balanced by kinetic friction acting up the slope. The normal reaction balances only the perpendicular component of weight, not the whole weight.

Question 26Mechanics

A force of 20 N acts on a 4.0 kg object for 3.0 s. What is the change in momentum of the object?

  1. 12 kg m/s
  2. 5.0 kg m/s
  3. 60 kg m/s Correct answer.
  4. 240 kg m/s

Explanation

Impulse equals force multiplied by time, so the change in momentum is 20 × 3.0 = 60 kg m/s. The mass is not needed for this calculation because impulse directly gives the change in momentum. Using F = ma would give the same result after first finding the acceleration.

Question 27Mechanics

Why is a tall, narrow box more likely to topple than a short, wide box of the same mass when both are tilted?

  1. Its weight is larger.
  2. Its base area is larger.
  3. Its mass is concentrated lower.
  4. Its centre of gravity is higher. Correct answer.

Explanation

A taller box has its centre of gravity higher above the base, so a smaller tilt moves the vertical line through the centre of gravity outside the base. Once that line falls outside the base, the weight creates a turning moment that topples the box. A wider base increases stability because it allows a larger tilt before this happens.

Question 28Mechanics

A stone tied to a string is whirled in a horizontal circle at constant speed. The string suddenly breaks. In which direction does the stone move immediately after the string breaks?

  1. Tangent to the circle Correct answer.
  2. Spirally outward from the centre
  3. Along the original circular path
  4. Radially outward from the centre

Explanation

At any instant the stone's velocity is tangential to the circle. When the string breaks there is no inward force to change the direction of motion, so by Newton's first law the stone continues along the tangent at that instant. The outward sensation during circular motion is not a real outward force on the stone.

Question 29Mechanics

A pendulum bob is released from rest at a height h above its lowest point and reaches speed v at the lowest point. Ignoring air resistance, from what height must it be released to reach speed 2v at the lowest point?

  1. h/2
  2. 2h
  3. 4h Correct answer.
  4. 8h

Explanation

Conservation of energy gives mgh = ½mv², so the speed squared is proportional to the drop height. To double the speed, v² must become four times larger, so the height must be four times larger, 4h. The mass cancels and does not affect the result.

Question 30Mechanics

Two point masses are separated by a distance r. If each mass is doubled and the separation is halved, by what factor does the gravitational force between them change?

  1. 16 Correct answer.
  2. 4
  3. 8
  4. 2

Explanation

Newton's law of gravitation gives F proportional to m1 m2 / r². Doubling each mass multiplies the numerator by 4, while halving the separation multiplies the denominator by 1/4, which multiplies the force by 4. The two effects combine to give a factor of 16.

Question 31Mechanics

Two forces of 3.0 N and 4.0 N act at right angles to each other at a point. What is the magnitude of their resultant?

  1. 12.0 N
  2. 5.0 N Correct answer.
  3. 7.0 N
  4. 1.0 N

Explanation

Perpendicular vectors add by Pythagoras, so the resultant magnitude is the square root of 3.0 squared plus 4.0 squared. This gives the square root of 25, which is 5.0 N.

Question 32Mechanics

A passenger standing in a bus tends to lurch forward when the driver applies the brakes sharply. Which statement best explains this?

  1. The passenger tends to continue moving forward while the bus slows. Correct answer.
  2. The passenger's inertia decreases when the bus brakes.
  3. A forward force from the braking system acts directly on the passenger.
  4. The passenger is pushed forward by the air inside the bus.

Explanation

By Newton's first law, an object continues in uniform motion unless a resultant external force acts on it. When the bus decelerates, the passenger tends to keep moving forward at the original speed, so the passenger appears to lurch forward relative to the bus.

Question 33Mechanics

A car doubles its speed while its mass remains constant. By what factor does its kinetic energy change?

  1. A factor of 1
  2. A factor of 0.5
  3. A factor of 4 Correct answer.
  4. A factor of 2

Explanation

Kinetic energy is given by KE = 1/2 mv^2, so it is proportional to the square of the speed. Doubling the speed multiplies v^2 by 4, making the kinetic energy four times larger when the mass is unchanged.

Question 34Mechanics

A ball is projected horizontally from the top of a table. Air resistance is negligible. Which quantity is determined by the table height and the gravitational field strength alone?

  1. The horizontal velocity of the ball
  2. The total mechanical energy of the ball
  3. The horizontal range of the ball
  4. The time taken to reach the floor Correct answer.

Explanation

The vertical motion is independent of the horizontal motion and starts with zero vertical velocity. Using h = 1/2 gt^2, the fall time depends only on the height h and the gravitational field strength g.

Question 35Mechanics

Two trolleys are initially at rest and held together against a compressed spring. When released, the 2.0 kg trolley moves left at 1.5 m/s. The other trolley has mass 1.0 kg. What is its velocity immediately after release?

  1. 0.0 m/s
  2. 3.0 m/s to the right Correct answer.
  3. 1.5 m/s to the right
  4. 0.75 m/s to the right

Explanation

The total momentum before release is zero, so the total momentum after release must also be zero. The 2.0 kg trolley has momentum 3.0 kg m/s to the left, so the 1.0 kg trolley must have momentum 3.0 kg m/s to the right, giving 3.0 m/s.

Question 36Mechanics

A uniform metre rule of weight 1.0 N is pivoted at the 40 cm mark. A 2.0 N weight hangs from the 10 cm mark. What downward force at the 80 cm mark will keep the rule horizontal?

  1. 3.00 N
  2. 0.50 N
  3. 2.00 N
  4. 1.25 N Correct answer.

Explanation

Take moments about the pivot at 40 cm. The 2.0 N weight has moment 2.0 × 0.30 = 0.60 N m anticlockwise, while the rule's weight has moment 1.0 × 0.10 = 0.10 N m clockwise. For balance, F × 0.40 + 0.10 = 0.60, giving F = 1.25 N.

Question 37Mechanics

A skydiver falls from rest and eventually reaches terminal velocity. Which statement is correct at terminal velocity?

  1. The skydiver's acceleration is equal to g.
  2. The air resistance is zero.
  3. The resultant force on the skydiver is zero. Correct answer.
  4. The skydiver's weight is smaller than usual.

Explanation

At terminal velocity the upward air resistance has increased until it equals the skydiver's weight. The resultant force is therefore zero, so the acceleration is zero and the speed remains constant.

Question 38Mechanics

A solid block floats in water with 60% of its volume below the surface. The density of water is 1000 kg/m^3. What is the density of the block?

  1. 600 kg/m^3 Correct answer.
  2. 1000 kg/m^3
  3. 400 kg/m^3
  4. 1670 kg/m^3

Explanation

For a floating object, the upthrust equals its weight. The upthrust equals the weight of displaced water, so density of block × total volume = density of water × submerged volume. With 60% submerged, the block's density is 0.60 × 1000 = 600 kg/m^3.

Question 39Mechanics

A small ball attached to a string of length 0.50 m is whirled in a vertical circle. What minimum speed must the ball have at the highest point for the string to remain taut? Take g = 10 m/s^2.

  1. 5.0 m/s
  2. 2.2 m/s Correct answer.
  3. 7.1 m/s
  4. 0.0 m/s

Explanation

At the highest point, the minimum condition for the string to stay taut is that the tension just becomes zero, so the weight alone provides the centripetal force. Then mg = mv^2/r, giving v = square root of gr = square root of 5.0, which is about 2.2 m/s.

Question 40Mechanics

A satellite orbits a planet in a circular orbit of radius r with period T. A second satellite orbits the same planet with orbital radius 4r. What is the period of the second satellite?

  1. 16T
  2. 4T
  3. 8T Correct answer.
  4. 2T

Explanation

Kepler's third law states that the square of the orbital period is proportional to the cube of the orbital radius. Increasing r by a factor of 4 increases T by 4^(3/2), which is 8, so the period becomes 8T.

Question 41Mechanics

A student is describing the motion of a stone falling freely from rest. Which of the quantities listed is a scalar?

  1. Acceleration
  2. Velocity
  3. Displacement
  4. Mass Correct answer.

Explanation

A scalar quantity is completely specified by a magnitude and a unit, so the mass of the stone needs only a number such as 0.20 kg. Velocity, displacement and acceleration each also require a direction, which makes them vectors. The mass is therefore the only scalar in the list.

Question 42Mechanics

A 3.0 kg trolley moving at 4.0 m/s along a straight track collides with a stationary 1.0 kg trolley. The trolleys stick together on impact. What is the common speed of the trolleys immediately after the collision?

  1. 2.0 m/s
  2. 3.0 m/s Correct answer.
  3. 4.0 m/s
  4. 1.0 m/s

Explanation

In the absence of an external horizontal force, total momentum is conserved: (3.0 kg)(4.0 m/s) = 12 kg m/s before impact. After the collision the combined mass is 4.0 kg, so the common speed is 12 kg m/s divided by 4.0 kg, giving 3.0 m/s. Kinetic energy is not conserved here because the trolleys stick together, but momentum is.

Question 43Mechanics

A rope pulls a sledge with a force of 50 N directed at 30° above the horizontal. What is the horizontal component of this force?

  1. 50 N
  2. 29 N
  3. 25 N
  4. 43 N Correct answer.

Explanation

The horizontal component is found by resolving the force with the cosine of the angle it makes with the horizontal, so Fx = 50 cos 30°. Since cos 30° = 0.866, the component is about 43 N. Using the sine would give the vertical component, 25 N, instead.

Question 44Mechanics

A car of mass 1200 kg travels at a constant speed of 20 m/s around a horizontal bend of radius 50 m. What is the resultant force on the car?

  1. 9.6 kN away from the centre of the bend
  2. 24 kN towards the centre of the bend
  3. 9.6 kN towards the centre of the bend Correct answer.
  4. 480 N towards the centre of the bend

Explanation

For motion in a circle the resultant force is the centripetal force, of magnitude mv²/r, directed towards the centre of the circle. Substituting gives (1200 kg)(20 m/s)² / 50 m = 9600 N, or about 9.6 kN. This force is provided by friction between the tyres and the road.

Question 45Mechanics

A 2.0 kg block on a smooth horizontal table is connected by a light string passing over a frictionless pulley to a 3.0 kg hanging mass. Taking g = 10 m/s², what is the acceleration of the system when it is released?

  1. 10 m/s²
  2. 12 m/s²
  3. 6.0 m/s² Correct answer.
  4. 4.0 m/s²

Explanation

The only unbalanced force driving the system is the weight of the hanging mass, 3.0 kg × 10 m/s² = 30 N. This force must accelerate both masses together, a total of 5.0 kg, because they are joined by the taut string. Applying Newton's second law gives a = 30 N / 5.0 kg = 6.0 m/s².

Question 46Mechanics

A ball is kicked from level ground with a speed of 20 m/s at 30° above the horizontal. Air resistance is negligible. How long does the ball take to reach the highest point of its path? (Take g = 9.8 m/s².)

  1. 2.0 s
  2. 1.0 s Correct answer.
  3. 0.87 s
  4. 0.51 s

Explanation

The time to reach the highest point depends only on the vertical component of velocity. This component is u_y = 20 sin 30° = 10 m/s. At the highest point the vertical velocity is zero, so t = u_y / g = 10 / 9.8 ≈ 1.0 s. The horizontal component affects the range but not the time taken to rise to the top.

Question 47Waves, Sound and Light

Sound waves travelling through air are best described as which type of wave?

  1. Longitudinal Correct answer.
  2. Transverse
  3. Stationary
  4. Electromagnetic

Explanation

In a sound wave the air particles oscillate parallel to the direction in which the wave travels, so it is longitudinal. Sound needs a material medium and is not an electromagnetic wave.

Question 48Waves, Sound and Light

Which value is the typical speed of sound in air at room temperature?

  1. 3.0 × 10^8 m/s
  2. 1500 m/s
  3. 340 m/s Correct answer.
  4. 34 m/s

Explanation

Sound travels through air at roughly 340 m/s at room temperature. The much larger figure 3.0 × 10^8 m/s is the speed of light in a vacuum.

Question 49Waves, Sound and Light

A light ray strikes a plane mirror at 30° to the normal. What angle does the reflected ray make with the normal?

  1. 90°
  2. 60°
  3. 30° Correct answer.
  4. 0°

Explanation

The law of reflection states that the angle of incidence equals the angle of reflection, both measured from the normal. Since the incident ray is 30° from the normal, the reflected ray is also 30° from the normal.

Question 50Waves, Sound and Light

A student claps and hears the echo from a distant wall 0.80 s later. If sound travels at 340 m/s, how far is the student from the wall?

  1. 425 m
  2. 68 m
  3. 136 m Correct answer.
  4. 272 m

Explanation

The sound travels to the wall and back, so the total distance is v × t = 340 × 0.80 = 272 m. The one-way distance is half of this, giving 136 m.