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 5 s. The car traveled ___ m after the brakes were applied.
Hint:
50 m
The correct answer is: 50
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/s2
Therefore, the acceleration of the car is - 4 m/s2.
On using the second equation of motion we get,
s = ut + ½at2
Or, s = 20 x 5 + ½ (- 4) (5)2
Or, s = 100 - 50
Or, s = 50 m
Therefore, the distance covered by the car is 50 m.
Negative acceleration is known as deceleration.
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