Newton's Laws of Motion & Momentum (OCR A Level Physics): Exam Questions

A bicycle manufacturer carries out tests on the braking system of their new model.

A cyclist on this new bicycle travels at a constant initial speed U.

The cyclist applies the brakes at time t = 0 and the bicycle comes to a stop at time t = 2.0 s.

Fig. 20.1 shows the variation of the braking force F on the bicycle with time t.

Fig. 20.1

Use Newton’s second law of motion to explain the physical quantity represented by the area under the graph shown in Fig. 20.1.

The total mass of cyclist and bicycle is 71 kg.

Use Fig. 20.1 to calculate the initial speed U.

U = .................................. ms^–1   

Complete Fig. 20.2 to show the variation of the speed of the bicycle from t = 0 to t = 2.0 s.

Fig. 20.2

A helium atom X travelling at 610 m s⁻¹ makes an elastic collision with a stationary helium atom Y. The magnitude of the velocity of X after the collision is 258 m s⁻¹.

 The directions of the velocities of X and Y are as shown in Fig. 22.

Fig. 22

i) Explain what is meant by an elastic collision.

 [1]

ii) The mass of a helium atom is 6.64 × 10⁻²⁷ kg.

 Calculate the magnitude of the momentum p of Y after the collision.

p = ............................................ kg m s⁻¹ [3]

There is a lot of helium in the Universe. This was also true of the Earth when it was formed billions of years ago. However, only small traces of helium are now found in the atmosphere of the Earth.

Use the kinetic theory of gases to explain why only small amounts of helium are found in the Earth’s atmosphere. Use the information below to do suitable calculations to support your answer.

• typical atmospheric temperature = 10°C

• mass of helium atom = 6.64 × 10⁻²⁷ kg

• escape velocity from the Earth = 11 km s⁻¹

Two gliders, A and B, are on a horizontal air track.

The gliders collide. A variable force is exerted on glider B by glider A during the collision, reaching a maximum force of magnitude 40 N. The collision lasts 0.4 s.

(i) Sketch a graph on the axes below to show the variation of force with time .

[2]

(ii) Use Newton's second law to explain the physical quantity represented by the area under your graph in (i).

[2]

Glider A has a mass of and moves towards glider B with a velocity of .

Glider B has a mass of and is initially at rest.

(i) State the principle of conservation of momentum.

[2]

(ii) Calculate the velocity of glider A immediately after the collision.

[2]

The gliders collided head on.

(i) Describe the difference between an elastic collision and an inelastic collision.

[1]

(ii) Determine whether the collision is elastic or inelastic.

[3]

State one assumption made about the forces acting on the gliders during the collision in your calculations for (b).