Question

A tennis ball of mass 0.25kg strikes the racket at speed of 20m/s . The player returns the ball which goes back in opposite direction after it is hit. If the ball remains in contact which the racket for 0.1s . What is the force that acts on the ball?

Answer 1

Since here collision is taking place,we have to consider the momentum.According to Newton's second law a change in momentum is caused by a force.Using this equation f=dp/dt

Answer 2

Answer: 100 N of force acts on the tennis ball.

Explanation:

Momentum of a body is defined as the product of its mass and velocity.

It is a vector quantity and denoted by p

p = mv

m ⇒ mass of body

v ⇒ velocity of body

Momentum and force are related by the Newton's second law.

According to Newton's second law, force acting on a body is equal to its rate of change of momentum.

$F =\frac{dp}{dt}$

If no force acts on a body then momentum of the body remains constant.

Let the direction away from racket be positive.

Mass of tennis ball(m) = 0.25 kg

Initial velocity of tennis ball (u) = 20 m/s towards racket

Initial velocity of tennis ball (u) = -20 m/s

Initial momentum of tennis ball = mu = 0.25 × (-20) kgm/s

Initial momentum of tennis ball =  - 5 kgm/s

Final velocity of tennis ball (v) = 20 m/s away from racket

Final velocity of tennis ball (v) = 20 m/s

Final momentum of tennis ball = mv = 0.25 × 20 kgm/s

Initial momentum of tennis ball = 5 kgm/s

Change in momentum =  Final momentum - Initial momentum

Change in momentum (Δp) =  5 - (-5)  = 10 kgm/s

Time for which contact occurred (Δt) = 0.1 s

Force on tennis ball = Δp/Δt = 10/0.1 N = 100 N

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