A satellite is revolving round the earth in an elliptical orbit, then
a) gravitational force exerted by the earth is equal to centripetal force at some points only
b) power associated with gravitational force is zero at every point
c) workdone by gravitational force is zero in some small parts of the orbit
d) at some points, the magnitude of gravitational force is greater than that of centripetal force

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only a and b are true

only b&c are true

only a,b & d are true

only a,c,d are true

answer is D.

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Detailed Solution

At Perigee and apogee , gravitational force is normal to the tangent drawn to the elliptical path so gravitational force is the centripetal force acting on the planet at these two points only.

At Perigee and apogee , angle between gravitational force acting on plant and velocity vector of planet is 90⁰ , so work done by gravitational force on the planet is zero at these two points.

At all points , except at perigee and apogee , normal component of gravitational force is centripetal force.

for example At B , $\vec{F_{g}} = \vec{F_{1}} + \vec{F_{2}}$ and F₂ does work on the satellite andF_g > F₁ .