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Standard IX

Physics

Equations of Motion

A man is movi...

Question

A man is moving with 36 kmph. The time of reaction is 0.9 seconds. On seeing an obstacle in the path, he applies brakes and decelerates at 5 m/s², the total distance covered before he stops is:

18 m

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17 m

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16 m

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19 m

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Solution

The correct option is D
19 m

Given

u = 10 m/s

Distance covered within reaction time, d = u x t = 10 x 0.9 = 9 m

a = -5 m/s²

v = 0 m/s

we know that, a = (v - u) / t.

So, t = (v - u) / a = (-10)/(-5) = 2s

We also know that, the distance is given as

s = ut + (1/2) at²

s = (10) (2) + (1/2) (-5)(2)(2)

s = 20 + (-10) = 10

Total displacement = 9 + 10 = 19

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A man is moving with 36 kmph. The time of reaction is 0.9 seconds. On seeing an obstacle in the path, he applies brakes and decelerates at 5 m/s2, the total distance covered before he stops is:

A man is moving with 36 kmph. The time of reaction is 0.9 seconds. On seeing an obstacle in the path, he applies brakes and decelerates at 5 m/s², the total distance covered before he stops is: