Q. If suppose moon is suddenly stopped and then released (given radius of moon is one-fourth the radius of earth)and the acceleration of moon with respect to earth is 0.0027 $ms^{- 2}$), then the acceleration of the moon just before striking the earth’s surface is (Take g = 10 $ms^{- 2}$)
A) $0.0027\ ms^{- 2}$
B) $5.0\ ms^{- 2}$
C) $6.4\ ms^{- 2}$
D) $10\ ms^{- 2}$
Explanation
(c) Just before striking, the distance between the centre of earth and moon is,
$r = R_{e} + \frac{R_{e}}{4} = \frac{5R_{e}}{4}$
So, acceleration of moon at this moment is
$a = \frac{GM_{e}}{\left( 5R_{e}/4 \right)^{2}\ } = \frac{16}{25} \times 10 = 6.4\ ms^{- 2}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.