An object of mass 20 kg is dropped from a height of 4 m. Fill in the blanks
in the following table by computing
the potential energy and kinetic
energy in each case.
E + EK
P
Height at
which object
is located
Potential Kinetic
energy energy
(E = mgh) (E = mc2/2)

Just above
the ground
For simplifying the calculations, take
the value of g as 10 m s2

PE = 800j, KE = 800J

Explanation:

To calculate the potential energy, we use the formula  

Potential Energy = Mgh

M = 20kg, g = 10m/sˆ2 , h = 4m

=20 × 10 × 4

=800J

At the maximum height  S = 4 and the initial velocity u = 0 The acceleration g = 10m/sˆ2

Using the third equation of motion

vˆ2 = uˆ2 + 2as

= 0ˆ2 + 2 × 10 ×  4

vˆ2 = 80

Kinetic Energy (KE) is given by  

KE = ½ mvˆ2

= ½ × 20 × 80

=800J