18 pdf a) A car starts from rest, and then begins driving with a constant accele

Question

18 pdf a) A car starts from rest, and then begins driving with a constant acceleration of 4.0 m/s2 south for 2.0 seconds. What is the car's velocity at the end of this acceleration, written in tems of components (in the usual cordinates)? b) A ball rolls straight down a ramp, starting from rest, and taking 0.73 s to reach the bottom. The ramp is 2.0 ft tall, and 5.0 ft wide horizontally. The ball's speed at the bottom of the hill is 8.0 ft/s. What was the magnitude and direction of the ball's average acceleration? Initial

Explanation / Answer

(a) a = - 4 m/s^2 j

v = v0 + a t

v = 0 + (-4j x 2) = - 8 j

Ans: v = (-8 m/s) j

(b) Applying vf = v0 + a t

8 = 0 + a(0.73)

a = 10.96 ft/s^2 (down the incline)

(Or tan^-1(2/5) = 21.8 deg below the horizontal)

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