1. 1
   At a shipping port, a crane's electric motor accelerates a loaded shipping container of mass 2000 kg from rest along a horizontal rail, increasing its velocity from 0 to 4 m/s in 8 s.

   (a)

   Which equation links resultant force, mass and acceleration (Newton's Second Law)?

   [1 mark]

   • AF = ma
   • BF = m/a
   • CF = a/m
   • DF = m + a

   (b)

   What is the correct SI unit for acceleration?

   [1 mark]

   • Am/s
   • Bm/s²
   • Ckg m/s
   • DN/kg

   (c)

   Calculate the container's acceleration.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A cyclist and bike, of total mass 70 kg, ride along a flat straight road. Initially the driving force from pedalling equals the resistive forces (air resistance and friction), so she travels at a constant speed. She then pedals harder, increasing the driving force to 140 N while the resistive forces remain at 100 N.

   (a)

   While the driving force equals the resistive force, Newton's First Law states that the cyclist will:

   [1 mark]

   • Aaccelerate forward
   • Bdecelerate
   • Ccontinue at the same constant velocity
   • Dimmediately stop

   (b)

   What is the resultant (unbalanced) force acting on the cyclist once she increases her driving force to 140 N, with resistive forces remaining at 100 N?

   [1 mark]

   • A240 N forward
   • B0 N
   • C100 N backward
   • D40 N forward

   (c)

   Calculate the cyclist's acceleration once the resultant force acting on her is 40 N forward (total mass 70 kg). Give your answer to 2 significant figures.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   In the 1940s, engineers testing an early rocket on a launch stand study how the rocket's engine produces thrust by expelling hot exhaust gases downward at high speed.

   (a)

   Explain, using Newton's Third Law, how the rocket is able to accelerate upward by expelling exhaust gases downward, even though there is no surrounding air or surface for it to push against.

   [3 marks]

   (b)

   The rocket has a mass of 500 kg (excluding fuel already burnt) and the engine produces a thrust force of 6000 N upward. The rocket's weight is 4900 N. Calculate the resultant force on the rocket and its acceleration, and state the direction of the acceleration.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Two ice skaters, of different masses, stand facing each other at rest on frictionless ice. Skater A (mass 50 kg) pushes against Skater B (mass 70 kg), and both skaters glide apart in opposite directions.

   (a)

   Explain, using Newton's Third Law and the idea of interaction pairs, why both skaters move apart after Skater A pushes against Skater B, and explain why the two skaters end up moving at different speeds despite experiencing forces of equal magnitude.

   [6 marks]

   (b)

   If the push results in each skater experiencing a force of 210 N for 0.3 s, calculate the acceleration of each skater during the push and the velocity each skater reaches, and use these values to justify your explanation of why the lighter skater moves away faster.

   [6 marks]

   Total for question 4: 12 marks

End of questions