The roller coaster below starts at a height of 70m, and initial velocity of 20m/

Question

The roller coaster below starts at a height of 70m, and initial velocity of 20m/s What is the fastest speed the roller coaster reaches? _____ What is the speed at the end of the ride? _____ During practice a tennis player practices her serves by hitting a tennis ball towards the wall. The player hits the ball with a speed of 30m/s, and the ball bounces back with a speed of 20m/s, and the contact time of the ball and the wall is .12 seconds. Solve for the impulse force the wall exerts on the ball: _____

Explanation / Answer

M = 4000 kg, hi = 70 m , vi = 20 m/s

(a) from conservation of energy

(K1 +U1) = (K2 +U2)

0.5Mvi^2 +Mghi = 0.5Mv^2 +0

0.5*20*20 + 9.8*70 = 0.5*v^2

v = 42.1 m/s

(b) from conservation of energy

K1 +U1 = K2 +U2

(0.5*mvi^2) +Mghi = 0.5Mv^2 +Mgh

0.5*20*20 + 9.8*70 = 0.5*v^2 + 9.8*10

v = 39.7 m/s

5) u = - 30 m/s, v = 20 m/s, t = 0.12 s

force = m(v-u)/t

m = mass of tennis ball

F = m(20+30)/0.12

F = m*417

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