1. An athlete runs a certain rest before taking a long jump. Why?
An athlete runs a certain distance to accelerate himself and gain enough momentum so that he can jump through the maximum possible length.
2. Springs are provided in car seats. Why?
The springs in the car seats absorb shock (sudden jumps) due to the roughness of the road. Thus, making the ride more comfortable.
3. A gun of mass 1500 kg fires a shell of mass 15kg with velocity 150 m/s. calculate velocity of recoil of the gun.
Before firing, total momentum of the gun and shell is = 0 (they were all at rest)
After firing, the momentum of the shell = 15 X 150 = 2250 Ns
The momentum of the gun is = 1500v Ns
By conservation of momentum,
Total momentum before firing = Total momentum after firing
=> 0 = 2250 + 1500v
=> v = -2250/1500 = -1.5 m/s
The negative sign implies the recoil velocity of the gun is opposite to the velocity of the shell.
4. Why cricketer pulls his hands backwards while catching the ball
Ans: cricketer pulls his hands backwards while catching the ball. When he does so, momentum of the ball reduces slowly, and time t required for this increases. As per F =DP/t , as t increase, magnitude of F decreases. As a result cricketer can catch the ball, easily, without any injury.
5. Why A karate player in order to break a brick, hits it quickly.
Ans: A karate player in order to break a brick, hitsit quickly, so in a short time there is a large change
in momentum and as per F =change in p/t as large force acts on the brick and it breaks.
6. What is impulse of Force?
Ans: Product of force and the time period for which force is acting is called impulse of force. If, on an object, Force F acts for time t. Then Impulse of force = force x time
I = F x t= change in p
Like force, impulse of force is also a vector quantity. Direction of impulse of force is same as the direction of force. Unit of impulse of force is kg m/s or Ns.
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