Question

You pull your hands back while catching a fast moving cricket ball. Which law is used to explain it?
A. law of inertia
B. Newton’s second law of motion
C. Newton’s first law of motion
D. Newton’s third law of motion

Answer 1

Hint: When we try to catch a ball with our hands then we are actually trying to stop the motion of the ball by allowing the ball to transfer its momentum to our hands. Now if the momentum transfer takes place in a long duration of time then the force exerted on our hands will be less. By studying this principle, we need to see which law of motion can best explain this phenomenon.

Complete answer:
Newton’s second law of motion states that the force applied on a body is directly proportional to the acceleration of the body. Mathematically, it is given as
\[F = ma\]
This law can also be understood in terms of the change in momentum to the body according to which, the force exerted by a body is equal to the rate of change of the momentum of the body.
$F = \dfrac{{dp}}{{dt}}$
When we try to catch a fast moving cricket ball with our hands then we are actually trying to stop the motion of the ball we do by allowing the ball to transfer all its momentum to our hands. Now if we try to catch the ball by keeping our hands fixed in place then the momentum transfer to our hand takes place in a very short interval of time and according to the above expression, the force exerted by the ball on our hands will be very large.
But if we try to catch the ball by moving our hand backwards then the momentum transfer takes place in a long duration of time and the force exerted on our hands will be less.

Hence, the correct answer to the question is option B.

Note:
It should be noted that the first law of motion is related with the inertia of the body which is the tendency of a body to stay in a state of rest or of uniform motion in the absence of an external force. The third law is related to the fact that to every action, there is an equal but opposite reaction force.