Kinetic and gravitational potential energyIB MYP Physics: Subtopic test

1. 1
   A student in Nairobi throws a 0.50 kg ball straight up into the air from ground level with an initial speed of 12 m/s. Take g = 10 N/kg.

   (a)

   Ignoring air resistance, what is the kinetic energy of the ball as it leaves the student's hand?

   [1 mark]

   • A36 J
   • B3.0 J
   • C6.0 J
   • D72 J

   (b)

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

   [1 mark]

   • A3.6 m
   • B14.4 m
   • C7.2 m
   • D72 m

   (c)

   Describe the energy transfers that happen as the ball rises to its highest point and then falls back to the ground.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A roller-coaster car and its passengers have a total mass of 400 kg. The car is released from rest at the top of a hill that is 25 m above the lowest point of the track at a theme park in Dubai. Take g = 10 N/kg.

   (a)

   What is the gravitational potential energy of the car at the top of the hill, relative to the lowest point of the track?

   [1 mark]

   • A10 000 J
   • B100 000 J
   • C4000 J
   • D250 J

   (b)

   Assuming there is no friction, what is the speed of the car at the lowest point of the track?

   [1 mark]

   • A16 m/s
   • B250 m/s
   • C500 m/s
   • D22 m/s

   (c)

   In reality the car reaches the lowest point moving more slowly than the speed predicted when friction is ignored. Explain why.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A class investigates how the height from which a steel ball is dropped affects its speed just before it hits the ground. The ball has a mass of 0.050 kg and light gates measure its speed just before impact. The measured speeds were 1.9 m/s from a height of 0.20 m, 2.8 m/s from 0.40 m, 3.4 m/s from 0.60 m, 3.9 m/s from 0.80 m and 4.4 m/s from 1.00 m. Take g = 10 N/kg.

   (a)

   Identify the independent variable, the dependent variable and one control variable in this investigation.

   [3 marks]

   (b)

   For the drop from 1.00 m, calculate the gravitational potential energy lost by the ball and the kinetic energy it gains. Suggest why the two values are not equal.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A city council in India is considering lowering the speed limit on a busy road that passes three schools, from 60 km/h to 30 km/h. A typical car on the road has a mass of 1200 kg. A speed of 60 km/h is about 16.7 m/s and 30 km/h is about 8.3 m/s.

   (a)

   Calculate the kinetic energy of a typical car at each speed. State how many times greater the kinetic energy is at 60 km/h, and explain why this makes lower speeds safer for children near the schools.

   [6 marks]

   (b)

   Discuss and evaluate the council's proposal to lower the speed limit to 30 km/h.

   [6 marks]

   Total for question 4: 12 marks

End of questions