A particle of mass m is driven by a machine that delivers a constant power k watts. If the particle starts…

A particle of mass m is driven by a machine that delivers a constant power k watts. If the particle starts from rest the force on the particle at time t is:
  1. mk2t12
  2. mk t-12
  3. 2mk t-12
  4. 12mk t-12

Solution

$\begin{aligned} & F v=\text{constant}=k \\ & \text{So}, \\ & \frac{m dv}{d t} v=k \\ \Rightarrow & \int v dv=\int \frac{k}{m} dt \\ \Rightarrow & \frac{v^2}{2}=\frac{k}{m} t \\ \Rightarrow & v=\sqrt{\frac{2 k}{m} t} \end{aligned}$ Now, $\begin{aligned} & F=\frac{m dv}{d t} \\ & =m \sqrt{\frac{2 k}{m}} \frac{1}{2} t^{-\frac{1}{2}} \\ & =\sqrt{\frac{m k}{2}} t^{-\frac{1}{2}} \end{aligned}$

Asked in: NEET 2015 (Phase 1)

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