9. Applications of second law

1. A fielder in the cricket ground pulls his hands backwards with the fast-moving cricket ball during the action of catching. By this action, the fielder prolongs the time to decrease the velocity of the fast-moving ball to zero. Hence, the impact of catching the fast-moving ball is reduced by decreasing the acceleration of the ball.

 

 

If the fielder suddenly stops the ball, its high velocity drastically decreases to zero in a very short period.

 

As a result, the rate of change of momentum will be large, and thus, a large force should be exerted for taking the catch that may hurt the fielder's palm.

 

2. Athletes in high jump sporting events are forced to land on a cushioned or a sand bed. This is done to prolong the time it takes for the athlete's fall to come to a halt after completing the jump. An increase in the time of fall reduces the force by lowering the rate of change of momentum.

 

 

3. With the same technique, a karate player breaks an ice slab with a powerful single blow.

 

 

From the second law's mathematical expression, the first law of motion can be easily stated.

 

 

When the force $F$ is zero, the final velocity is equal to the initial velocity ($v =u$), whatever the time $t$ may be.

 

Hence, it implies that the object will continue its motion with uniform velocity, $u$ throughout the time, $t$. If $u$ is zero, then $v$ will also be zero, keeping the object at rest.