When serving a tennis ball, a player hits the ball when its velocity is zero (at

Question

When serving a tennis ball, a player hits the ball when its velocity is zero (at the highest point of a vertical toss). The racquet exerts a force of 564 N on the ball for 4.76 ms, giving it a final velocity of 44.3 m/s. Using these data, find the mass (in g) of the ball. ____________ g A baseball with a mass of 135 g is thrown horizontally with a speed of 41.0 m/s (92 mi/h) at a bat. The ball is in contact with the bat for 1.15 ms and then travels straight back at a speed of 45.9 m/s (103 mi/h). Determine the average force exerted on the ball by the bat. Neglect the weight of the ball (it is much smaller than the force of the bat) and choose the direction of the incoming ball to be positive. ___________ Can you write an expression for the average force exerted on the ball in terms of its change in momentum and the time the force acts? Can you write and expression for the change in momentum? Pay careful attention to the sign convention suggested in the statement of the problem. N

Explanation / Answer

4)

F = 564 N

time , t = 4.76 ms

v = 44.3 m/s

let the mass of ball is m

F = change in momentum/time

564 * 4.76 *10^-3 = m * (44.3)

m = 0.0606 Kg = 60.6 gm

the mass of ball is 60.6 gm
5)

m = 0.135 Kg

u = 41 m/s

v = 45.9 m/s

t = 1.15 ms

average force exerted = -m * (v + u)/time

average force exerted = -0.135 * (41 + 45.9)/(1.15 *10^-3)

average force exerted = -10201 N

the average force exerted is -10201 N

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