science

Grade-9

Easy

Question

# The driver of a car moving at a speed of 20 m/s applies the brakes on seeing a rock at some distance. The car stops after 12 s. The acceleration of the car is -___m/s^{2}.

Hint:

### 4 m/s²

## The correct answer is: 4

### Given that,

The initial velocity, u = 20 m/s

The final velocity, v = 0

Time taken, t = 5 s

On using the first equation of motion we get,

v = u + at

Or, a = (v – u)/t

Or, a = (0 – 20)/5

Or, a = - 20 / 5

Or, a = - 4 m/s^{2}

Therefore, the acceleration of the car is - 4 m/s^{2}.

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