Work, energy and conservation of energyEdexcel International A Level Physics: Subtopic test

1. 1
   A student pulls a sledge of mass 12 kg along level ground with a rope. The tension in the rope is 50 N and the rope makes an angle of 30° above the horizontal. The sledge moves 8.0 m from rest. A constant frictional force of 30 N opposes the motion.

   (a)

   What is the work done by the tension in the rope on the sledge over the 8.0 m?

   [1 mark]

   • A400 J
   • B200 J
   • C462 J
   • D346 J

   (b)

   What is the kinetic energy of the sledge after it has moved 8.0 m?

   [1 mark]

   • A106 J
   • B346 J
   • C240 J
   • D586 J

   (c)

   Calculate the speed of the sledge after it has moved 8.0 m.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A ball of mass 0.15 kg is thrown vertically upwards from ground level with an initial speed of 14 m s⁻¹. In a first model, air resistance is ignored. The acceleration of free fall is 9.81 m s⁻².

   (a)

   What is the kinetic energy of the ball when it is thrown?

   [1 mark]

   • A1.1 J
   • B14.7 J
   • C29.4 J
   • D2.1 J

   (b)

   Ignoring air resistance, what is the maximum height reached by the ball?

   [1 mark]

   • A1.4 m
   • B20.0 m
   • C10.0 m
   • D14.7 m

   (c)

   In practice the ball reaches a maximum height of only 9.0 m. Calculate the energy dissipated by air resistance as the ball rises.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A child of mass 30 kg slides from rest down a straight playground slide of length 4.0 m. The top of the slide is 2.5 m above the bottom. The child reaches the bottom at a speed of 5.0 m s⁻¹.

   (a)

   Calculate the energy dissipated as the child slides down the slide.

   [3 marks]

   (b)

   Calculate the average frictional force on the child along the slide, and state what happens to the energy dissipated.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A roller coaster car of total mass 500 kg is released from rest at the top of a track at a height of 40 m above its lowest point. The speed of the car at the lowest point is measured as 24 m s⁻¹.

   (a)

   Explain, using the principle of conservation of energy, why the speed of the car at the lowest point is less than the value expected if no energy were dissipated, and calculate that expected speed.

   [6 marks]

   (b)

   The car is now filled with passengers so that its total mass is 700 kg. A student claims that it will reach the same speed of 24 m s⁻¹ at the lowest point. Assume the energy dissipated by resistive forces is again 5.2 × 10⁴ J. Evaluate the student's claim.

   [6 marks]

   Total for question 4: 12 marks

End of questions