Physics Exercise 2.10

This is for those who didn't manage to jot down the questions in class earlier today. Solve the questions in your exercise books.

1. A crane lifts a load of 5000N through a vertical distance of 12m from a ship to the ground in 20s. Calculate the average power of the crane. [ Unit of Energy: Joule (J) ]

2. A rock of mass 4.5kg falls from a height of 14m to the ground. Calculate the loss of potential energy when the rock is 5m above the ground.

3. An electric motor lifts a box of mass 5.0kg to a height of 18m in 5s. Calculate the power of the motor.

4. A lift in a building can carry 15 people through a height of 10m in 10 seconds. The total mass of the lift and its passengers is 1500kg. Calculate the power of the lift.

5. A fat man of mass 100kg and a thin man of mass 50kg both ran up a flight of stairs at a height of 12m. Both the men took 10s to complete the task. Calculate the power generated by each man.

6. The graph in figure below shows the relationship between force, F and the spring extension, x.

Calculate the work done to stretch the spring from 8cm to 12cm.

7. An electric motor of a crane rated 500W can lift a load of 450N vertically through a height of 8m in 10s. Calculate the efficiency of the motor.

*Refer to your notebook if you're stuck at any question.