Forces, Newton's laws and free-body diagramsEdexcel A-Level Physics: Subtopic test

1. 1
   A book of mass 0.80 kg rests on a horizontal table.

   (a)

   Which set of forces acts on the book?

   [1 mark]

   • AIts weight downwards only
   • BIts weight downwards and the contact (normal) force from the table upwards
   • CIts weight downwards, the contact force upwards and the force of the book on the table downwards
   • DIts weight downwards, the contact force upwards and a friction force sideways

   (b)

   Which force forms a Newton's third law pair with the weight of the book?

   [1 mark]

   • AThe contact force of the table on the book
   • BThe force of the book on the table
   • CThe gravitational force of the Earth on the table
   • DThe gravitational force of the book on the Earth

   (c)

   Calculate the weight of the book and explain, using Newton's first law, why the contact force from the table has this same size.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A car of mass 1200 kg accelerates in a straight line from rest along a level road. Its engine produces a driving force of 3600 N and the resistive forces on the car total 600 N.

   (a)

   What is the resultant forward force on the car?

   [1 mark]

   • A3600 N
   • B4200 N
   • C3000 N
   • D600 N

   (b)

   What is the acceleration of the car?

   [1 mark]

   • A2.5 m s⁻²
   • B3.0 m s⁻²
   • C0.50 m s⁻²
   • D3.5 m s⁻²

   (c)

   At a higher speed the resistive forces rise to 3600 N while the driving force is unchanged. Describe and explain the motion of the car from this point.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A skydiver of mass 80 kg falls vertically with her parachute closed. At one instant her speed is 30 m s⁻¹ and the air resistance on her is 360 N.

   (a)

   Calculate the acceleration of the skydiver at this instant.

   [3 marks]

   (b)

   Explain why the skydiver eventually reaches a terminal velocity, and state the size of the air resistance when she does.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A passenger of mass 60 kg stands on bathroom scales on the floor of a lift. The lift and its contents have a total mass of 540 kg and are supported by a single cable. The lift moves vertically.

   (a)

   Explain how the force exerted by the scales on the passenger compares in three situations: the lift moving upwards at constant velocity, accelerating upwards at 1.5 m s⁻², and accelerating downwards at 1.5 m s⁻². Explain also why the reading on the scales is equal to this force.

   [6 marks]

   (b)

   The lift accelerates upwards at 1.5 m s⁻². Calculate the tension in the cable. The cable can safely provide a tension of at most 7000 N. Evaluate whether this acceleration is safe and find the greatest safe upward acceleration.

   [6 marks]

   Total for question 4: 12 marks

End of questions