Question

On a planet (whose size is the same and mass $4$ times as that of the earth), the energy needed to lift a $2kg$ mass vertically upwards through $2m$ distance is ($g=10$ $m/s^2$ on the surface of the earth)

• A. $16$ joule
• B. $160$ joule
• C. $32$ joule
• D. $320$ joule

Answer 1

The correct option is B $160$ joule

On the planet, $g^{\prime }=\frac{G\times 4M}{R^2}$

On the earth, $g=\frac{GM}{R^2}$

$\therefore \frac{g^{\prime }}{g}=4$

$\Rightarrow g^{\prime }=4g=40m/s^2$

Energy needed to lift $2kg$ mass through $2m$ distance,

$E=m{g}^{\prime }h$

$=2\times 40\times 2$

$=160$ joules.