PHYSICS-ASSIGNMENT

Chapter: Work and Energy Class: IX

Answer the following:

1. Explain the work done by the constant force, when the direction of the force and displacement may be –i) same ii) opposite iii) perpendicular to each other,iv) there may not be displacement at all

2. A coolie with a suitcase on his head is climbing up on a ladder with uniform speed. Explain the work done by the coolie on the suitcase.

3. Write the factors on which kinetic energy of the body depends.4. Which would have a greater effect on kinetic energy of an object, doubling the mass

or doubling the velocity?5. Give one example of each the following

i) when body possess kinetic energyii) when body possess potential energyiii) when body possess both, kinetic energy as well as potential energy.

6. Two bodies A and B of equal masses are kept at heights of hand 2h respectively. What will be the ratio of their potential energy?

7. Two bodies A and B of equal masses are moving with uniform speed of v and 2v respectively. What will be the ratio of their kinetic energy?

Solve the following:

1. A body of mass 2 kg is thrown vertically upwards with an initial velocity of 20m/s. What will be its potential energy at the end of 2s?(g= 9.8m/s2 )(Answer: 400J)

2. A man drops a 10 kg rock from the top of a 5 m ladder. What is its speed just before it hits the ground? What is its kinetic energy when it reaches the ground? ( g= 10m/s2) (Answer: 500J)

3. A boy weighing 40 kg makes a high jump of 4m. (g=10m/s2)i) What is his kinetic energy at the middle of the high jump?ii) What is his potential energy at the highest point? (Answer: 800J, 1600J)

4. A man exerts a force of 200N in pulling a cart at a constant speed of 16m/s. Calculate the power spent by the man. (Answer: 3.2kW )

5. A 60 kg person climbs stairs of total height 20m in 2 min. Calculate the power delivered.(Answer: 100W)

6. An electric bulb of 60 W is used for 6h per day. Calculate the ‘units’ of energy consumed in one day by 5 such bulbs. (g=10m/s2)(Answer: 18 units)