MomentumIB MYP Physics: Subtopic test

1. 1
   A cricket coach in Chennai studies a ball of mass 0.16 kg that is bowled along a straight line at 30 m/s towards a batter. The batter hits the ball straight back along the same line at the same speed.

   (a)

   Which statement about momentum is correct?

   [1 mark]

   • AIt is a scalar quantity because it depends only on mass and speed
   • BIt is measured in newtons
   • CIt is the product of mass and acceleration
   • DIt is a vector quantity with both size and direction

   (b)

   What is the momentum of the ball as it is bowled?

   [1 mark]

   • A187.5 kg m/s
   • B4.8 kg m/s
   • C30.16 kg m/s
   • D0.0053 kg m/s

   (c)

   Taking the direction in which the ball was bowled as positive, state the momentum of the ball after it is hit. Explain why it is different from the momentum before, although the speed is the same.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Two trolleys are on a level, low-friction laboratory track. Trolley X has a mass of 2.0 kg and moves at 3.0 m/s towards trolley Y, which has a mass of 1.0 kg and is at rest. When they collide they stick together and move off along the track as one object.

   (a)

   Which quantity is the same just before the collision and just after it?

   [1 mark]

   • AThe total momentum of the two trolleys
   • BThe velocity of trolley X
   • CThe total kinetic energy of the two trolleys
   • DThe momentum of trolley X alone

   (b)

   What is the total momentum of the two trolleys just after the collision?

   [1 mark]

   • A3.0 kg m/s
   • B9.0 kg m/s
   • C6.0 kg m/s
   • D2.0 kg m/s

   (c)

   Calculate the velocity of the two trolleys just after the collision.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A group of students investigates how the force on a hand catching a ball depends on the time the ball takes to stop. A ball of mass 0.40 kg is thrown at 5.0 m/s into a hand holding a force sensor. When the hand is held rigid, the ball stops in 0.05 s. When the hand moves backwards with the ball, the ball stops in 0.20 s.

   (a)

   State the independent variable and the dependent variable. Write a testable hypothesis for this investigation and give a scientific reason for it.

   [3 marks]

   (b)

   Calculate the average force on the ball in each case. Decide whether the results support the idea that a longer stopping time gives a smaller force, and suggest one way to make the investigation more reliable.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A car manufacturer in Seoul designs cars with crumple zones and air bags. In a crash test, a car of mass 1000 kg travelling at 20 m/s hits a solid wall and stops. A car with a rigid front stops in 0.10 s, but a car with a crumple zone stops in 0.50 s. The government is considering making crumple zones and air bags compulsory in all new cars sold in the country.

   (a)

   Calculate the average force on each car during the crash, and use your results to explain how a crumple zone reduces the risk of injury to the passengers.

   [6 marks]

   (b)

   Discuss and evaluate the government's proposal to make crumple zones and air bags compulsory in all new cars.

   [6 marks]

   Total for question 4: 12 marks

End of questions