Chapter 4 Physic Solved Exercise 

“Work And Energy”

1. A person holds a bag of groceries while standing still, taking to a friend. A car is stationary with the engine running. From the stand point of work, how are these two situations similar?
2. Calculate the work done in kilo joules in lifting a mass of 10 kg (at steady velocity) through a vertical height of 10 m.
3. A force F acts through a distance L. The force is them increase to 3F, and then acts through a further distance of 21. Draw the work diagram to scale.
4. In which case is more word done? When a 50 kg bag of books is lifted through 50 cm, or when a 50 kg crate is pushed through 2m across the floor with a force of 50 N.
5. An object has 1 J of potential energy. Explain what does it mean?
6. A ball of mass m is held at a height h1 above a table. The table top is at a height h2 above the floor. One student says that the ball has potential energy mgh1 but other says that is is mg(h1+h2). Who is correct?
7. When a rocket re-enters the atmosphere, its nose cone become very hot. Where does this heat energy come from?
8. A girl drops a cup from a certain height, which breaks into pieces. What energy changes are involved?
9. A boy uses a catapult to throw a stone which accidentally smashes a green house window. List the possible energy changes.