Question

A body of mass $500g$ is thrown upward with a velocity $20m/s$ and reaches back to the surface of a planet after $20$ sec Then the weight of the body on that planet is :

• A. $2N$
• B. $4N$
• C. $5N$
• D. $1N$

Answer 1

The correct option is D $1N$

The acceleration when the mass is going up is given as,

$v^2=u^2+2as$

${\left(20\right)}^2={\left(0\right)}^2+2as$

$a=\frac{200}{s}$ (1)

The acceleration when the mass is going down is given as,

$s=\frac{1}{2}a{t}^2$

$s=\frac{1}{2}a{\left(10\right)}^2$

$a=\frac{s}{50}$ (2)

From equation (1) and (2), we get

$\frac{200}{s}=\frac{s}{50}$

$s=100m$

Substitute the value of $s$ in the equation (2), we get

$a=\frac{100}{50}$

$=2m/s^2$

The weight is given as,

$W=0.5\times 2$

$=1N$

Thus, the weight of the body on that planet is $1N$.