Question

A body of mass 2 kg is thrown vertically upwards with an initial velocity of 20 m/s. What will be its potential energy at the end of 2 s? (Assume g = 10 m/s²).

Answer 1

Mass of the body, (m) = 2 kg
Initial velocity of the body, (u) = 20 m/s
Time, (t) = 2s
Acceleration due to gravity, (g) = 10 m/s²
Let the height attained at the end of 2 s be (s)
We will use the second equation of motion to find the height of the body,
$$\begin{gathered} s=ut+\frac{1}{2}a{t}^2 \\ \mathrm{So}, \\ s=20\left(2\right)+\frac{1}{2}(-10)(2{)}^2 \\ =(40–20)\mathrm{m} \\ =20\mathrm{m} \end{gathered}$$
(We have taken a negative because it is opposite in direction to the initial velocity)
We can calculate potential energy as,
P.E = (m) (g) (h)
So,
P.E = 2 × 10 × 20 J
$=\boxed{400\mathrm{J}}$