Discuss whether or not work is done in the following cases:
(i) When we twist a wire.
(ii) When we press a football.
(iii) When we push a table.
(iv) When a person carries a handbag and walks on a level road.
(v) When a person holds a book in his hand and keeps it stationary.

A car weighing 1000 kg and travelling at 30 m/s stops at a distance of 50 m decelerating uniformly. What is the force exerted on it by the brakes?What is the work done by the brakes?

Define the term energy.Give some examples of bodies possessing some energy.

What is the work to be done to increase the velocity of a car from 30 km h^–1 to 60 km h^–1 if the mass of the car is 1500 kg?

A body of mass 25 kg is raised to the top of a building 10 m high and then dropped freely under gravity.
(a) Calculate the work done in raising the body to the top of the building.
(b) What is the value of the gravitational potential energy at the top of the building?
(c) By what factor will the gravitational potential energy of the same body increase if it is raised to the top of a multistorey building 30 m high?
(d) When will the kinetic energy of the body be maximum?

Name and define the SI unit of power.Give some bigger units of power.

A 100 W electric bulb is lighted for 2 hours every day and five 40W tubes are lighted for 4 hours everyday. Calculate
(i) the energy consumed for 60 days and the
(ii) cost of electricity consumed at the rate of Rs.3 per kWh.

Look at the activities listed below. Reason out whether or not work is done in the light of your understanding of the term 'work':
(i) Suma is swimming in a pond.
(ii) A donkey is carrying a load on its back.
(iii) A wind-mill is lifting water from a well.
(iv) A green plant is carrying out photosynthesis.
(v) An engine is pulling a train.
(vi) Food grains are getting dried in the sun.
(vii) A sailboat is moving due to wind energy.

Certain force acting on a 20 kg mass changes its velocity from 5 ms^-1 to 2 ms^-1 .Calculate the work done by the force.

An object of mass 40 kg is raised to a height of 5m above the ground.What is its potential energy?If the object is allowed to fall, find its kinetic energy when it is half-way down.