A tractor of 3,000 kg, moving at a constant speed of 20 m/s stops after covering some distance. The force applied by the brakes is 24,000 N. Compute the time taken by the truck to stop after the brake is applied.
A
-2.5 s
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B
6 s
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C
5 s
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D
2.5 s
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Solution
The correct option is D 2.5 s Given, m = 3,000 kg, F = 24,000 N, u = 20 m/s, v = 0 m/s (stops)
a = F/ m = - (24,000)/3,000 = -8 m/s−2 [Negative sign because of retardation, truck stops, velocity decreases]
Newton’s 1st law of motion v = u + at
0 = 20 + (-8 m/s−2) t
t = 2.5 s