1. A ball of dough is rolled into a flat chapatti. Name the force exerted to change the
shape of the dough.
Ans. Muscular force.
2. Where do we apply a force while walking?
Ans. While walking we apply force on the ground.
3. A girl is pushing a box towards east direction. In which direction should her friend
push the box so that it moves faster in the same direction?
Ans. Towards east.
4. During dry weather, clothes made of synthetic fibre often stick to the skin. Which
type of force is responsible for this phenomenon?
Ans. Electrostatic force.
5. While sieving grains, small pieces fall down. Which force pulls them down?
Ans. Force of gravity.
6. Does force of gravity act on dust particles?
Ans. Yes
7. A gas filled balloon moves up. Is the upward force acting on it larger or smaller than the force of gravity?
Ans. Upward force is larger than the force of gravity.
8. Does the force of gravitation exist between two astronauts in space?
Ans. Yes
9. A chapati maker is a machine which converts balls of dough into chapatti’s. What
effect of force comes into play in this process?
Ans. The force changes the shape of the dough.
10.
Fig. shows a man with a parachute. Name the force which is responsible for his
downward motion. Will he come down with the same speed without the parachute?
Ans. Force of gravity. No, without the parachute his speed will be higher.
11. Two persons are applying forces on two opposite sides of a moving cart. The cart still
moves with the same speed in the same direction. What do you infer about the
magnitudes and direction of the forces applied.
Ans. Both the forces are of equal magnitudes and applied in the opposite directions.
12. Two thermocol balls held close to each other move away from each other. When they
are released, name the force which might be responsible for this phenomenon.
Explain.
Ans. Electrostatic force. The balls have similar charges. They move away due to repulsion
between similar charges.
13. Fruits detached from a tree fall down due to force of gravity. We know that a force
arises due to interaction between two objects. Name the objects interacting in this
case.
Ans. Earth and fruits.
14. A man is pushing a cart down a slope. Suddenly the cart starts moving faster and he
wants to slow it down. What should he do?
Ans. He should apply a force to pull the cart up the slope.
15. An archer shoots an arrow in the air horizontally. However, after moving some
distance, the arrow falls to the ground. Name the initial force that sets the arrow in
motion. Explain why the arrow ultimately falls down.
Ans. The archer stretches the string of the bow by applying muscular force. In this
process the shape of the bow changes. When the string is released, it regains its
original position that provides the initial force to set the arrow in motion. The force of
gravity that acts on the arrow in the downward direction brings it to the ground.
16. It is difficult to cut cloth using a pair of scissors with blunt blades. Explain.
Ans. Blunt blades have larger area compared to the sharp-edged blades. Thus, the
applied force produces a lower pressure in case of blunt blades, which makes it
difficult to cut the cloth.
17. Two women are of the same weight. One wears sandals with pointed heels while the
other wears sandals with flat soles. Which one would feel more comfortable while
walking on a sandy beach?Give reasons for your answer.
Ans. The woman wearing sandals with flat soles will feel more comfortable while walking
on the sandy beach. The flat soles have larger area compared to the sandals with
pointed heels. Since the two women are of the same weight, they will apply same
force on the ground. Therefore, the pressure exerted by the pointed heels will be
more compared to that with sandals having flat soles. As a result the pointed heel
sandals will sink more in the sand than the flat sole sandals. Hence, walking with
flat sole sandals will be more comfortable.
18. It is much easier to burst an inflated balloon with a needle than by a finger. Explain.
Ans. When we prick the surface of an inflated balloon with a needle it exerts a larger
pressure because it has a smaller area of contact compared to the finger. The large
pressure pierces the surface of the balloon easily.
19. Will force of friction come into play when a rain drop rolls down a glass window
plane?
Ans. Yes.
20. Two boys are riding their bicycles on the same concrete road. One has new tyres on
his bicycle while the other has tyres that are old and used. Which of them is more
likely to skid while moving through a patch of the road which has lubricating oil
spilled over it?
Ans. The bicycle with worn out tyres is more likely to skid.
21. Imagine that an object is falling through a long straight glass tube held vertical; air
has been removed completely from the tube. The object does not touch the walls of
the tube. Will the object experience any force of friction?
Ans. No
22. You might have noticed that when used for a long time, slippers with rubber soles
become slippery. Explain the reason.
Ans. When rubber soles are used for a long time, their surfaces become smooth. Hence,
the friction between the sole and the floor decreases. Therefore, slippers become
slippery.
23. Is there a force of friction between the wheels of a moving train and iron rails? If yes,
name the type of friction. If an air cushion can be introduced between the wheel and
the rail, what effect will it have on the friction?
Ans. Yes, rolling friction. If an air cushion is introduced between the wheel and the rails,
the friction will decrease.
24. Cartilage is present in the joints of our body, which helps in their smooth movement.
With advancing age, this cartilage wears off. How would this affect the movement of
joints?
Ans. The wearing off of cartilage will increase the friction. As a result the movement of
joints will become difficult which may lead to joint pains.
25. The handle of a cricket bat or a badminton racquet is usually rough. Explain the
reason.
Ans. To increase friction between handle of the bat and hands, to have a better grip.
26. Explain why the surface of mortar and pestle (silbatta) used for grinding is etched
again after prolonged use?
Ans. To increase friction to make it more effective for grinding again.
27. A marble is allowed to roll down an inclined plane from a fixed height. At the foot of
the inclined plane, it moves on a horizontal surface
(a) covered with silk cloth
(b)covered with a layer of sand
(c) covered with a glass sheet.
On which surface will the marble move the shortest distance. Give reason for your answer.
Ans. On the surface covered with sand, it will cover the least distance because sand offers
maximum friction against its motion.
28. A father and son pushed their car to bring it to the side of road as it had stalled in
the middle of the road. They experienced that although they had to push with all
their might initially to move the car, the push required to keep the car rolling was
smaller, once the car started rolling. Explain.
Ans. Because initially they had to apply force to set the car in motion but once the car
started rolling, they had to apply force only to balance rolling friction of the car, the
value of which is very less.
29. When the cutting edge of a knife is put against a fast rotating stone to sharpen it,
sparks are seen to fly. Explain the reason.
Ans. Friction between grinding stone and the cutting edge of the knife produces heat. As
the friction is very large in this case, a large amount of heat is produced and we see
sparks flying.
30. We have two identical metal sheets. One of them is rubbed with sand paper and the
other with ordinary paper. The one rubbed with sand paper shines more than the
other. Give reason.
Ans. The friction between sand paper and metal sheet is very large, compared to that
between the ordinary paper and the metal sheet. Thus the sand paper is able to
remove the outer dull layer from the metal sheet more effectively and makes it more
shining.
31. While travelling on a rickshaw, you might have experienced that if the seat cover is
very smooth, you tend to slip when brakes are applied suddenly. Explain.
Ans. If the seat cover is very smooth then the friction between our body and the seat is
very small. Therefore, when the brakes are applied we tend to slip.
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