Question

A tennis ball and a cricket ball, both are stationary. To start motion in them
A) less force is required for a cricket ball than for a tennis ball.
B) less force is required for a tennis ball than for a cricket ball.
C) Same force is required for both the balls.
D) Nothing can be said.

Answer 1

Here we have to find the force required to start motion in the balls which are at rest. As from the first law of motion a body will remain at rest until force is applied. The force required can be given from the second law of motion.

Complete answer:
Newton’s first law of motion states that the body will remain at rest or in motion unless some force is applied. Here the two balls are at rest and from the first law they will require some force to start the motion.
Now the second law of motion says that the force is the product of mass of the body and the acceleration of the body. The body will have acceleration if it is in motion. Hence from the second law we can find the force required to start the motion. The mathematical representation of the law is
$F=ma$

From the above equation we can say that the force is directly proportional to the mass of an object, the heavier object will require more force to start the motion and the lighter object will require less force.
If mass of tennis ball is ${{m}_{T}}$, the mass of the cricket ball is ${{m}_{C}}$, the force require for tennis ball is ${{F}_{T}}$and the force require for the cricket ball is ${{F}_{C}}$, as

& {{m}_{C}} > {{m}_{T}} \\\ & {{F}_{C}} > {{F}_{T}} \\\ \end{aligned}$$ Hence less force is required for a tennis ball than a cricket ball. **So, the correct answer is “Option B”.** **Note:** In case there were two cricket balls then both the ball would require the same force and the golf ball would require more force as compared to the cricket ball as it is heavier than it. Newton’s second law is valid only for the constant mass, an object which has variable mass can’t be defined from the second law of motion.