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Question

Brakes are applied to a car moving with disengaged engine, bringing it to a halt after 2 s. What is it's velocity at the moment when the breaks are applied if the coefficient of friction between the road and the tyre is 0.4?

A
3.92ms1
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B
7.84ms1
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C
11.2ms1
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D
19.6ms1
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Solution

The correct option is B 7.84ms1
We have:
Frictional force =ma
μmg=ma=mvt
v=μgt
=0.4×9.8×2=7.84 m/s

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