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# Physics - Momentum/Impulse Question watch

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1. A tennis ball with no initial horizontal velocity leaves a tennis raquet with a horizontal speed of 58ms^-1. The mass of the ball is 0.060kg.

a) calculate the impulse given to the ball

i understand that impulse = change of momentum; impulse = 58 * 0.060; = 3.48kgms^-1

b) if the time of contact with the racquet is 0.025 s, calculate the average force exerted on the ball.

impulse = force * time; 3.48 * 0.025; but this doesn't seem to be the correct answer. Any suggestions?
2. (Original post by nofronting)
A tennis ball with no initial horizontal velocity leaves a tennis raquet with a horizontal speed of 58ms^-1. The mass of the ball is 0.060kg.

a) calculate the impulse given to the ball

i understand that impulse = change of momentum; impulse = 58 * 0.060; = 3.48kgms^-1

b) if the time of contact with the racquet is 0.025 s, calculate the average force exerted on the ball.

impulse = force * time; 3.48 * 0.025; but this doesn't seem to be the correct answer. Any suggestions?
The impulse = 3.48 so force = 3.48/0.025 = 139.2
3. (Original post by nofronting)
A tennis ball with no initial horizontal velocity leaves a tennis raquet with a horizontal speed of 58ms^-1. The mass of the ball is 0.060kg.

a) calculate the impulse given to the ball

i understand that impulse = change of momentum; impulse = 58 * 0.060; = 3.48kgms^-2

b) if the time of contact with the racquet is 0.025 s, calculate the average force exerted on the ball.

impulse = force * time; 3.48 * 0.025; but this doesn't seem to be the correct answer. Any suggestions?
b) impulse = F*t
t= 0.025
impulse = 3.48

i.e. 3.48 = F * 0.025
i.e F= 139.2

Is that better?
4. Aha, solved by units, but i still don't "understand" how to get to the answer.

b) if the time of contact with the racquet is 0.025 s, calculate the average force exerted on the ball.

impulse = force * time; 3.48 * 0.025; but this doesn't seem to be the correct answer. Any suggestions?

unit of force = N(kgms^-2); unit of time = second(s).
we know that the unit of an impulse is: kgms^-1. The get the units to kgms^-1 i would have to divide kgms^-1 into s which is equal to kgms^-1; so the force exerted on the ball is the the impulse/momentum divided into the time of contact with the ball.
5. Yeah, thanks.

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