Question

when a body of mass 2.5 kg is dropped from height 20m, it achieves speed of 3m/s. What is work done by body against air resistance?
Answer only if you know !​

Answer 1

Given that,

• Mass of the body = 2.5 kg (m)

• Height = 20 m (h)

• Speed or velocity of the body = 3 m/s (v)

We know that,

⇒ W.D ( air resistance ) + W. D ( gravity ) = ΔK.E

⇒ W.D against the resistance = -(1/2mv² - mgh)

⇒ W.D against the resistance = -(1/2×2.5×(3 m/s)²-2.5 kg×3 m/s×20 m)

⇒ W.D against the resistance = -(3.75-150) Joules

⇒ W.D against the resistance = -(-146.25) Joules

⇒ W.D against the resistance = +146.25 Joules.

∴ The work done against the air resistance is 146.25 Joules.

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