B) Kinetic Energy - the energy an object possesses due to its' motion
Work/KE
W = Fd = ∆KE
F = average Force W neg : decrease KE W + : increase KE
Ex) A softball having a mass of .25 kg is pitched at 95 km/hr. By the time it reaches the plate the ball slowed to by 10%. Neglecting gravity, estimate the average force of friction if the distance to the plate = 15 m W = Fd = ∆KE 95 km/hr [1000m/1km][1 hr/3600 sec] = 26.39 m/s = V1
slowed to by 10% .9[26.39 m/s] = 23.75 m/s = V2 ∆KE = 1/2m[V22 - V12 ] Fd = ∆KE F = ∆KE/d
F = -1.1 N
p. 162) 20
Ex) baseball (m = 140 g) travelling 32 m/s caught by a glove and moves glove back 25 cm. Average F of ball on glove?
Work of glove on ball = ΔKE
Wball = Fd = ∆KE
Fd = 1/2m[V22 - V12 ]
F[.25m] = 1/2[.14kg][0 - (32m/s)2 ] Fball[.25m] = -72 J Fball = -2.9 x 102 N Average F of ball on glove? Fglove = 2.9 x 102 N
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