A bird hits the windscreen of a fast moving car and falls on the bonnet. Which of the two, bird or car, suffer a grater change in momentum?

A bowler runs a long distance before bowling from the bowling line. Why ?

A piece of paper can be jerked out from under a book quickly without moving the book. Why?

Why is your foot hurt more when you kick a stone than when you hit a football?

State Newton’s third law of motion.

Define force. List any two effects of force.

Give reason: sparks produced in a grinding stone move tangentially.

A ball moving on a surface stops after travelling some distance. Does it violate the first law of motion? Explain.

A bullet of mass 10 g is fired horizontally with a velocity of 150 ms^–1 from a pistol of mass 2 kg. Find the recoil of the pistol.

A body at rest opposes the force which tries to move it. Name this property and give two examples to illustrate it.

Observe the following v-t graphs and explain the type of force acting in the cases given:

Give reasons for the following:

(a) A ball thrown upwards in a running train returns back to the hands.

(b) When a person moves out of a boat, it moves backward.

(a) Write an activity to demonstrate balanced and unbalanced forces.

(b) State whether the forces are balanced or unbalanced in each case:

(i) Suitcase dropped from a height.

(ii) A bicycle moving with constant velocity on a straight road.

(iii) The rope does not move in a tug of war on applying force at both ends.

State and prove the law of conservation of linear momentum.

Sonam was reading about balanced and unbalanced forces. She read that the gravitational force of sun and moon also acts on us. She wondered why we don’t fly towards these bodies. Her teacher, however, listened to her patiently and stored her doubts.

(a) What values of Sonam do you observe?

(b) Throw light on characteristic values of her teacher.

(c) Distinguish between balanced and unbalanced forces.

(d) What explanation would you give towards Sonam’s questions?

(e) Good reading habits lead to constructive learning. Comment.