Question

A body of mass $1kg$ is thrown vertically with an initial speed of $5m{s}^{-1}$. What is the magnitude and direction of force due to gravity acting on the body when it is at its highest point ? Take $g=9.8N$ $k{g}^{-1}$.

• A. $1$kgf or $9.8N$ vertically upwards.
• B. $1$kgf or $9.8N$ vertically downwards.
• C. $9.8$kgf or $1N$ vertically downwards.
• D. $9.8$kgf or $1N$ vertically upwards.

Answer 1

Answer: (B)

$1$kgf or $9.8N$ vertically downwards.

When is it at highest point its velocity becomes zero at that point. We know that $F=m\times a$. On substituting mass as 1 Kg and acceleration at that point is nothing but acceleration due to gravity which is always directed downward. Give $g=9.8m/s^2$. Hence Force is equal to $F=1\times 9.8$ newton. Hence answer is 9.8 newton.