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JAMB Physics 2012 Paper

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Question : 3

Total: 42

Calculate the total distance covered by a train before coming to rest if its initial speed is 30ms^-1 with a constant retardation of 0.1m^-2

5500m
4500m
4200m
3000m

Solution:

Concept:

Use

v^2 = u^2 + 2as

for motion with uniform acceleration. Retardation means acceleration is negative.

Explanation:

The train comes to rest, so final speed

v = 0\ \mathrm{m\,s^{-1}}

.

Initial speed

u = 30\ \mathrm{m\,s^{-1}}

.

Retardation is

0.1\ \mathrm{m\,s^{-2}}

, hence acceleration

a = -0.1\ \mathrm{m\,s^{-2}}

.

Substitute the values into

v^2 = u^2 + 2as

:

0^2 = 30^2 + 2(-0.1)s

0 = 900 - 0.2s

0.2s = 900

s = \frac{900}{0.2} = 4500\ \mathrm{m}

Answer:

B.

4500\ \mathrm{m}

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