Laws of motion class 11

Question 1

What gives the measure of inertia?

Answer 1

mass of a body

Question 2

mass and inertia relation

Answer 2

mass directly proportional to inertia

Question 3

Action reaction forces do not balance each other why?

Answer 3

when one body exerts a force on another body it gets equal and opposite reaction. The action and reaction forces do not cancel out each other since they do not act on the same body.

Question 4

it’s greater the attraction of 10KG mass for Earth or The Earth’s attraction for ten kg mass?

Answer 4

both are equal

Question 5

can a body remain in the state of rest of an external forces acting on it ?explain your answer

Answer 5

yes, if the external force acting on the body can be represented in magnitude and direction by the sides of a closed polygon taken in the same order.

Question 6

Name the physical situation when the mass of the body will change with time.

Answer 6

When the body moves with the speed comparable to the speed of light.
For example the mass of a charged particle increases when it moves in a cyclotron.

Question 7

Why a horse cannot pull a cart and run in the
empty space?

Answer 7

To pull the cart, a horse pushes the ground in
backward direction with its feet. The reaction from the ground
makes the cart to move forward. In an empty space, the horse
cannot push in backward direction and get a forward reaction.
That is why, a horse cannot pull a cart and run in the empty
space.

Question 8

it is easier to pull than to push a body. Explain.

Answer 8

When we pull a lawn roller, the vertical component
of the applied pull acts opposite to the weight of the roller and
it reduces its effective weight.

On the other hand, when a lawn roller is pushed, the
vertical component of the applied push adds to the weight of
the roller and hence its effective weight increases.

Thus, the effective weight is lesser, when the lawn roller
is pulled. Hence, itis easier to pull than to push a lawn roller.

Question 9

A stone when thrown on a glass window
smashes the window pane to pieces, but a bullet from the gun
passes through making a clean hole. Why ?

Answer 9

Ans. The velocity of the stone is much less than that of
the bullet fired from a gun. Due to its low speed, the stone
remains in contact with the window pane fora longer time and
its motion is shared by whole of the window pane. As a result,
it smashes into pieces. On the other hand, the bullet fired from
the gun remains in contact with the window pane for such a
small time that it can share its motion only with the portion of
the window pane, it comes in contact with. As such, it makes a
clean hole in the window pane.