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#3 | Work Done by Variable Force

(Physics) > Work,Energy and Power

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A body of mass *m* is moving in a circle of radius *r* with a constant speed *v*. The force on the body is $\frac{m{v}^{2}}{r}$ and is directed towards the centre. What is the work done by this force in moving the body over half the circumference of the circle

(1) $\frac{m{v}^{2}}{r}\times \pi r$

(2) Zero

(3) $\frac{m{v}^{2}}{{r}^{2}}$

(4) $\frac{\pi {r}^{2}}{m{v}^{2}}$

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When a body moves with a constant speed along a circle

(1) No work is done on it

(2) No acceleration is produced in the body

(3) No force acts on the body

(4) Its velocity remains constant

PMT - 1994

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A sphere of mass *m* is tied to end of a string of length *l* and rotated through the other end along a horizontal circular path with speed *v*. The work done by centripetal force in full horizontal circle is

(1) 0

(2) $\left(\frac{{\displaystyle m{v}^{2}}}{{\displaystyle l}}\right)\hspace{0.17em}.\hspace{0.17em}2\pi l$

(3) $\text{mg\hspace{0.17em}.\hspace{0.17em}2\pi l}$

(4) $\left(\frac{{\displaystyle m{v}^{2}}}{{\displaystyle l}}\right)\hspace{0.17em}.\hspace{0.17em}\left(l\right)$

PMT - 1993

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A body of mass 6*kg* is under a force which causes displacement in it given by $S=\frac{{t}^{2}}{4}$ *metres* where *t* is time. The work done by the force in 2 seconds is-

(1) 12 *J*

(2) 9 *J*

(3) 6 *J*

(4) 3 *J*

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