Page No 148:
Question 1:
A force of 7 N acts on an object. The displacement is, say 8 m, in the direction of the force (Fig. 11.3). Let us take it that the force acts on the object through the displacement. What is the work done in this case?
Page No 149:
Question 4:
A pair of bullocks exerts a force of 140 N on a plough. The field being ploughed is 15 m long. How much work is done in ploughing the length of the field?
Page No 152:
Question 3:
The kinetic energy of an object of mass, m moving with a velocity of 5 m s−1 is 25 J. What will be its kinetic energy when its velocity is doubled? What will be its kinetic energy when its velocity is increased three times?
Page No 156:
Question 3:
A lamp consumes 1000 J of electrical energy in 10 s. What is its power?
Page No 158:
Question 2:
An object thrown at a certain angle to the ground moves in a curved path and falls back to the ground. The initial and the final points of the path of the object lie on the same horizontal line. What is the work done by the force of gravity on the object?
Page No 158:
Question 5:
A mass of 10 kg is at a point A on a table. It is moved to a point B. If the line joining A and B is horizontal, what is the work done on the object by the gravitational force? Explain your answer.
Page No 158:
Question 6:
The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?
Page No 158:
Question 7:
What are the various energy transformations that occur when you are riding a bicycle?
Page No 158:
Question 8:
Does the transfer of energy take place when you push a huge rock with all your might and fail to move it? Where is the energy you spend going?
Page No 158:
Question 9:
A certain household has consumed 250 units of energy during a month. How much energy is this in joules?
Page No 158:
Question 10:
An object of mass 40 kg is raised to a height of 5 m 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.
Page No 158:
Question 11:
What is the work done by the force of gravity on a satellite moving round the earth? Justify your answer.
Page No 158:
Question 12:
Can there be displacement of an object in the absence of any force acting on it? Think. Discuss this question with your friends and teacher.
Page No 159:
Question 13:
A person holds a bundle of hay over his head for 30 minutes and gets tired. Has he done some work or not? Justify your answer.
Page No 159:
Question 14:
An electric heater is rated 1500 W. How much energy does it use in 10 hours?
Page No 159:
Question 15:
Illustrate the law of conservation of energy by discussing the energy changes which occur when we draw a pendulum bob to one side and allow it to oscillate. Why does the bob eventually come to rest? What happens to its energy eventually? Is it a violation of the law of conservation of energy?
Page No 159:
Question 16:
An object of mass, m is moving with a constant velocity, v. How much work should be done on the object in order to bring the object to rest?
age No 159:
Question 17:
Calculate the work required to be done to stop a car of 1500 kg moving at a velocity of 60 km/h?
Page No 159:
Question 19:
Soni says that the acceleration in an object could be zero even when several forces are acting on it. Do you agree with her? Why?
Page No 159:
Question 21:
A freely falling object eventually stops on reaching the ground. What happens to its kinetic energy?
