Newton’s Laws of Motion (AQA A Level Physics)

A car has a horizontal driving force of 8.0 kN acting on it and a resistive force a quarter of this size. It has a forward horizontal acceleration of 9.2 m s^–2.

What is the mass of the car?

In which of the following situations does the person concerned experience ‘weightlessness’?

A wooden block rests on a rough board. The end of the board is then raised until the block accelerates down the plane.

Which row describes the forces acting on the block when it is accelerating?

A block of mass 2.11 kg is on a rough horizontal surface. A force of 25 N is applied to the block and it accelerates at 6.0 m s^–2

What is the magnitude of the frictional force acting on the block?

Newton’s third law of motion is often summarised as

‘Every action has an equal and opposite reaction.’

A laptop rests on a table. If the weight of the laptop is the ‘action’ force, what is the ‘reaction’ force?

A bus is travelling forward at constant speed when a car collides with the bus perpendicularly to its direction of motion.

What is the effect of this force on the forward speed and sideways speed of this bus?

A rocket of mass 15 000 kg accelerates vertically upwards from the surface of the Earth at 2.5 m s^-2.

What is the thrust produced by the rocket?

The planets in our solar system travel around the Sun in an approximately circular orbit. The force of gravity, which keeps them orbiting, is due to the gravitational attraction between the planets and the Sun.

What would happen if the gravitational force between the planets and the Sun were to suddenly disappear?

A child playing in a toy car increases its speed from 2 m s^-1 to 5 m s^-1 in 3 s.

If the resultant force on the car is 40 N, what is the combined mass of the child and that car?

The mass of fuel in a racing car decreases during a race as it travels around multiple laps.

Which row describes what happens to its lap time and an explanation for this?

An object is stationary on an inclined slope at an angle θ to the horizontal. The frictional force along the slope is given by the equation:

frictional force = 0.34 × normal contact force

Which angle θ satisfies the equation given?

You may use the result:

Newton’s third law concerns the forces interacting with two bodies.

Which of the following statements relating to Newton’s third law is incorrect?

Two heavy ornaments are connected together and suspended in the corner of a room by cables. The mass of m₁ is three times greater than the mass of m₂. The system is in equilibrium.

What is the mass of m₁?

A van is parked on an icy slope and begins to slide with a constant acceleration of 1.2 m s^–2. There is a resistive force up the slope R, given by the expression ‘R = 2 × mass’.

What is the angle θ of the slope to the horizontal?

A spherical oil drop of mass 0.20 g and surface area of 314 mm² is falling vertically through water at a steady speed. The water has a viscosity η of 0.89 mPa s. The acceleration of freefall is g.

What gives the best estimate for the kinetic energy of the oil drop?

(The drag force on a falling sphere is given by Stokes’ Law: F = 6πr ηv)

A rocket takes off vertically by ejecting fuel downwards at a constant rate. Assume that g remains constant throughout the launch, and that the only forces acting on the rocket are its driving force and its weight.

 Which of these graphs shows the rocket’s acceleration–time graph during launch?

A 52 g conker is swung around in a vertical circle of radius 22 cm. It has a constant speed of 1.6 m s^–1.

What is the ratio of   at position X?

The diagram shows two masses, 15 kg and 20 kg respectively, joined by a light inextensible string which passes over a light frictionless pulley.

What is the acceleration of the masses the instant the 20 kg mass is released?