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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/$s^2$)
A
10 J
B
20 J
C
30 J
D
40 J
Detailed Solution
Initial kinetic energy: $K_i = \frac{1}{2}mu^2 = \frac{1}{2}\times1\times(20)^2 = 200$ J
At the highest point the body is at rest, so all its remaining energy is potential: $U = mgh = 1\times10\times18 = 180$ J
Energy lost due to air friction = initial energy − final energy
= 200 − 180
= 20 J
At the highest point the body is at rest, so all its remaining energy is potential: $U = mgh = 1\times10\times18 = 180$ J
Energy lost due to air friction = initial energy − final energy
= 200 − 180
= 20 J