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Scale Conversions

A 1500kg ca...

Question

A $1500$ kg car is moving at a uniform speed of $72 k m / h r$ .On applying brakes its speed is reduced to $18 k m / h$ .Calculate
(i) Initial K.E
(ii)Final KE and Change in KE

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Solution

$m = 1500 k g$
$v_{i} = 72 \times \frac{5}{18} = 20 m / s$

$v_{f} = 18 \times \frac{5}{18} = 5 m / s$

$(i) K E_{i} = \frac{1}{2} (1500) (20)^{2} = 300000 J$

$(i i) K E_{f} = \frac{1}{2} (1500) (5)^{2} = 18750 J$

$Δ K = K_{f} - K_{i} = - 281250 J$

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