Sports and Second Law of Motion


 
 
Concept Explanation
 

Sports and Second Law of Motion

Sports and Second Law of Motion

1.  A cricket player or fielder moves his hands backward while catching a fast cricket ball. This allows the fielder to catch the ball by applying a small force on it. If you keep your arms still while catching, the fielder has to apply a larger force on the ball. When we pull arms back with the ball. We apply a smaller force for a longer time. This is because the ball stops completely only when the hands stops moving.

Explanation: Suppose the ball is moving with a speed u. When it stops completely, its speed is v = 0.Suppose ,in the first case, when you pull your arms back, it takes time  t_1  to stop the ball. The acceleration of the ball in this period is 

                                          a_1:=:frac{v:-:u}{t_1}:=:frac{0:-:u}{t_1}:=:-frac{u}{t_1}

Similarly, if the time taken to stop the ball is t_2 in the second case,

                                         a_2:=:-frac{u}{t}

The force in the two cases are 

                              F_1:=;ma_1:=:-frac{mu}{t_1}         and      F_2:=;ma_2:=:-frac{mu}{t_2}

                                  therefore frac{F_1}{F_2}:=;frac{t_1}{t_2}

As t_1 is much larger than t_2, that force F_2 is much larger than F_1. A cricket coach, therefore , advise you to pull back your arms while taking a catch, as this would be easier.

2.  When an athlete jumps from a height on a hard surface, he can hurt his feet.

Explanation:

This is because the feet come to rest in a very short time and hence the force exerted on the feet is high. That is why athletes during high jump land on sand or foams. This increases the time in which the body comes to rest. The sand gives way allowing the body to slow down gradually.

 

Sample Questions
(More Questions for each concept available in Login)
Question : 1

A passenger in a moving train tosses a coin which falls behind him. Observing this statement what can you say about the motion of the train ?                               

Right Option : A
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Explanation
Question : 2

A goalkeeper in a game of football pulls his hands backwards after holding the ball shot at the goal. This enables the goalkeeper to  ___________________

 

Right Option : D
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Explanation
Question : 3

The unit of measuring the momentum of a moving  body is ______

Right Option : C
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Explanation
 
 
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