Question

A bicycle was travelling at 20 m/s when it applied its brakes and decelerated at a rate of
5m/s2. How long will it take before it comes to a stop?.
(A) 4sec
(B) 5 sec
(C)3 sec
(D) 6 sec
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Answer 1

Given :-

A  bicycle was travelling at 20 m/s when it applied its brakes and decelerated at a rate of  5m/s²

To Find :-

Time taken to stop

Solution :-

Since it come at rest. So, final velocity is 0

v = u + at

0 = 20 + (-5)(t)

0 - 20 = -5t

-20 = -5t

-20/-5 = t

20/5 = t

4 = t

Hence

Time taken to stop is 4 sec(Option A)

Answer 2

Answer:

(A) 4sec

Explanation:

initial velocity = 20m/s

final velocity = 0m/s ( as object comes to rest after applying brakes)

acceleration = -5m/s ( we will negative value as object decelerating to rest)

time = ?

By equation (i)

v = u + at

0 = 20 + (-5×t)

-20 = -5t

-20/-5 = t

4 = t

So,the time taken is 4 seconds