Question

Calculate the K.E and P.E. of the ball half way up, when a ball of mass $0.1kg$ is thrown vertically upwards with an initial speed of $20m{s}^{-1}$.

• A. $10J,20J$
• B. $10J,10J$
• C. $15J,8J$
• D. $8J,16J$

Answer 1

Answer: (B)

Total energy at the time of projection
$=\frac{1}{2}m{v}^2=\frac{1}{2}\times 0.1(20{)}^2=20J$
Half way up, P.E. becomes half the P.E. at the top i.e.
$\text{ P.E. }=\frac{20}{2}=10J$
$\therefore \text{ K.E. }=20-10=10J$