The crankshaft in a race car goes from rest to 3000 rpm in 3.0 s . (a) what is the crankshaft's angular acceleration?
(b) how many revolutions does it make while reaching 3000 rpm ?

75 rotations

Explanation:

f0 = 0, f = 3000 rpm = 50 rps, t = 3 s

(a) use first equation of motion for rotational motion

w = w0 + α t

2 x 3.14 x 50 = 0 + α x 3

α = 104.67 rad/s^2

(b) Let θ be the angular displacement

use second equation of motion for rotational motion

θ = w0 t + 1/2 α t^2

θ = 0 + 0.5 x 104.67 x 3 x 3

θ = 471.015 rad

The angle turn in one rotation is 2 π radian.

Number of rotation = 471.015 / (2 x 3.14) = 75 rotations

total distance/total time

(85 + 82)/(5+3)

167/8

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