First slide

Work

Question

The energy required to accelerate a car from 10 m/s to 20 m/s is how many times the energy required to accelerate the car from rest to 10 m/s

Moderate

A

Equal
B

4 times
C

2 times
D

3 times

Solution

Kinetic energy for first condition
$= \frac{1}{2} m (v_{2}^{2} - v_{1}^{2}) = \frac{1}{2} m (20^{2} - 10^{2}) = 150 mJ$
K.E. for second condition = $\frac{1}{2} m (10^{2} - 0^{2}) = 50 mJ$
$∴ \frac{(K . E .) I}{(K . E .) II} = \frac{150 m}{50 m} = 3$

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