A body of mass 1 kg is thrown upwards with a velocity 20 m/s. It momentarily comes to rest after attaining a height of 18 m. How much energy is lost due to air friction? (g = 10 m/s²)

Options

(a) 30 J
(b) 40 J
(c) 10 J
(d) 20 J

Correct Answer:

20 J

Explanation:

When the body is thrown upwards. its K.E is converted into P.E. The loss of energy due to air friction is the difference of K.E and P.E
1/2 mv² – mgh = 1/2 x 1 x 400 – 1 x 18 x 10
= 200 – 180 = 20 J