JEE Mains · Physics · STD 11 - Work,energy,power and collision
- JEE Mains 2020
- Hard
- Numerical
A body of mass \(2\, kg\) is driven by an engine delivering a constant 10.Power \(1\, J / s\). The body starts from rest and moves in a straight line. After \(9\) seconds, the body has moved a distance (in \(m )\)

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Answer & Solution
Correct Answer
(D) \(18\)
Step-by-step Solution
Detailed explanation
\(P=m a v\)
\(m \frac{d v}{d t} v=P\)
\(\int_{0}^{v} v d v=\frac{P^{t}}{m} \int_{0}^{t} d t\)
\(\frac{v^{2}}{2}=\frac{P t}{m} \Rightarrow v=\left(\frac{2 P t}{m}\right)^{1 / 2}\)
\(\frac{d x}{d t}=\sqrt{\frac{2 P}{m}} t^{1 / 2}\)
\(\int_{0}^{{x}} d x=\sqrt{\frac{2 P}{m}} \int_{0}^{t} t^{1 / 2} d t\)
\(x=\sqrt{\frac{2 P}{m}} \frac{t^{3 / 2}}{3 / 2}=\sqrt{\frac{2 P}{m}} \times \frac{2}{3} t^{3 / 2}\)
\(=\sqrt{\frac{2 \times 1}{2}} \times \frac{2}{3} \times 9^{3 / 2}\)
\(=\frac{2}{3} \times 27=18\)
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