Question

The brakes are set on a train at 30 mi. per hr., when ½ mi. from a station. The train slows down
uniformly, coming to rest at the station. Find the acceleration, and the time elapsed in stopping

Answer 1

Given info : The brakes are set on a train at 30 mi per hr, when ½ mi. from a station. The train slows down uniformly, coming to rest at the station.

To find : The acceleration, and time elapsed in stopping is..

solution : initial velocity of train, u = 30 miles/hr

final velocity of train, v = 0 [ because train finally comes to rest ]

distance covered by train to come to rest, s = 1/2 mile.

using formula, v² = u² + 2as

⇒0² = (30)² + 2 × a × 1/2

⇒-900 = a

⇒a = -900 miles/h²

Therefore acceleration of train is 900 miles/h²

now using formula, v = u + at

⇒0 = 30 miles/hr + (-900 miles/h²)t

⇒t = 1/30 hr = 2 minutes.

Therefore time elapsed in stopping is 2 minutes.

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