Question 1

Which of the following is a measure of inertia of a body?

Accepted Answer

Mass is the measure of inertia of a body. Greater the mass of a body, greater is its inertia, meaning it is more difficult to change its state of rest or uniform motion.

Question 2

Newton's first law of motion defines:

Accepted Answer

Newton's first law of motion defines inertia and force. It states that a body continues to remain in its state of rest or of uniform motion unless an external force acts on it.

Question 3

The rate of change of momentum of a body is directly proportional to the:

Accepted Answer

According to Newton's second law of motion, the rate of change of momentum of a body is directly proportional to the applied external force and takes place in the direction in which the force acts.

Question 4

Action and reaction forces:

Accepted Answer

According to Newton's third law, action and reaction forces act on two different bodies. Therefore, they never cancel each other out, even though they are equal in magnitude and opposite in direction.

Question 5

A bullet of mass 0.04 kg is fired from a gun of mass 20 kg. If the speed of the bullet is 300 m/s, the recoil speed of the gun is:

Accepted Answer

Using conservation of linear momentum: $m1 v1 + m2 v2 = 0$. Given $m1 = 0.04	ext{ kg}$, $v1 = 300	ext{ m/s}$, $m2 = 20	ext{ kg}$. $v2 = - \frac{0.04 	imes 300}{20} = -0.6	ext{ m/s}$. The magnitude is 0.6 m/s.

Laws of Motion