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5.work,energy,power and collision — Physics STD 11 Science — Question

Rajasthan BoardEnglish MediumSTD 11 SciencePhysics5.work,energy,power and collision1 Mark
MCQ
A body projected vertically from the earth reaches a height equal to earth's radius before returning to the earth. The power exerted by the gravitational force is greatest
  • A
    at the highest position of the body.
  • ✓
    at the instant just before the body hits the earth.
  • C
    it remains constant all through
  • D
    at the instant just after the body is projected.
✓

Answer

Correct option: B.
at the instant just before the body hits the earth.
b
Power, hitting $P=  \vec F\cdot \vec v  = 0 = Fv\cos\theta $
Just before hitting the earth $\theta =0^o$ Hence, the power exerted by the gravitational force is greatest at the instant just before the body hits the earth. 

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