The driver of a car moving at a speed of 10m/s applies the brakes after noticing an obstacle. The retardation due to the brakes is 4m/s2. What is the distance travelled by the car till it stops?
A
12m
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B
12.5m
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C
10m
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D
11m
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Solution
The correct option is B12.5m We know, u=10m/s a=−4m/s2
Let's say the car stops at ts
At ts, v=0 (because the car stopped)
Using the 1st equation v=u+at
We get, ⇒0=10+(−4)t ⇒4t=10 ⇒t=104=2.5s
To get the distance travelled by the car we can use the 2nd equation of motion s=ut+12at2
Replacing values of u, a and t in this equation, we get ⇒s=ut+12at2=(10×2.5)−12×4×2.52 ⇒s=12.5m