Question

Energy required to accelerate a car from $10 \,m / s$ to $20\, m / s$ compared with that required to accelerate it frem $0$ to $10 \,m / s$ is

• A. twice
• B. thrice
• C. four times
• D. same

Answer 1

Answer: (B)

thrice

Answer 2

$K E_{1} =\frac{1}{2} m\left(v_{2}^{2}-v_{1}^{2}\right)$ $\therefore K E_{1} =\frac{1}{2} m\left[(20)^{2}-(10)^{2}\right]$ $\Rightarrow K E_{1} =\frac{1}{2} m(400-100)$ $\Rightarrow K E_{1} =\frac{1}{2} m \times 300=150\, m$ ... (i) $K E_{2} =\frac{1}{2} m\left[(10)^{2}-0\right]$ $\Rightarrow KE _{2}=\frac{1}{2} m \times 100=50 \,m$ ... (ii) From Eqs. (i) and (ii), we have $KE _{1}=3 KE _{2}$