Question:

A body is moving unidirectionally under the influence of a constant power source. Its displacement in time t is proportional to :

Updated On: Mar 22, 2025
  • t2
  • t23t^\frac{2}{3}
  • t32t^\frac{3}{2}
  • t
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The Correct Option is C

Solution and Explanation

Given that the body moves under the influence of a constant power source, we aim to find the relation between the displacement s s and the time t t .

Step 1: Understanding the Relationship Between Power and Velocity
Power P P delivered to the body is constant and is given by:

P=Fv, P = Fv,

where:
- F F is the force acting on the body,
- v v is the velocity of the body.

Using Newton’s second law F=ma F = ma , where m m is the mass and a a is the acceleration, we have:

P=mav. P = mav.

Since power is constant, we can write:

P=mvdvdt. P = mv \frac{dv}{dt}.

Step 2: Integrating the Equation
Rearranging:

Pdt=mvdv. P \, dt = mv \, dv.

Integrating both sides:

Pdt=mvdv. \int P \, dt = \int mv \, dv.

This yields:

Pt=mv22    v2=2Ptm. Pt = \frac{mv^2}{2} \implies v^2 = \frac{2Pt}{m}.

Taking the square root:

v=2Ptm. v = \sqrt{\frac{2Pt}{m}}.

Step 3: Finding the Displacement
Velocity is the derivative of displacement with respect to time:

v=dsdt=2Ptm. v = \frac{ds}{dt} = \sqrt{\frac{2Pt}{m}}.

Rearranging and integrating:

ds=2Pmt1/2dt. ds = \sqrt{\frac{2P}{m}} \, t^{1/2} \, dt.

Integrating both sides:

st3/2. s \propto t^{3/2}.

Therefore, the displacement s s is proportional to t3/2 t^{3/2} .

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