According to recent test data, an automobile travels 0.250 mi in 19.9 s, startin

Question

According to recent test data, an automobile travels 0.250 mi in 19.9 s, starting from rest. The same car, when braking from 60.0 mi/h on dry pavement, stops in 146 ft. Assume constant acceleration in each part of the motion, but not necessarily the same acceleration when slowing down as when speeding up.


Part A
Find the acceleration of this car when it is speeding up.

Part B
Find the acceleration of this car when it is braking.

Part C
If its acceleration is constant, how fast (in mi/h ) should this car be traveling after 0.250 mi of acceleration? The actual measured speed is 70.0 mi/h; what does this tell you about the motion?

Part D
How long does it take this car to stop while braking from 60.0 mi/h?

Explanation / Answer

A)0.25mile=402.34m

s=0.5at2

a=2.032m/s2

B)v2-u2=2as

a=-u2/2s=8.08m/s2

C)v=u+at=at=40.44m/s=90.45mi/h

D)t=v/a=3.32s

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