Question

A 5 kg ball when falls through the height of 20m requires a speed of 10m/s find the work done by air resistance.​

Answer 1

AnSwer :

The balls starts falling from position 1, where it's speed is zero, hence kinetic energy is aslo zero.

${ \sf{K_{1} = 0J \: \: \: \: \: .......(1)}}$

During the downward motion of the ball, constant gravitational force mg acts downwards and bmair resistance R of unknown magnitude acts upwards.

The ball reaches position 20m below the position-1 with a speed v = 10m/s, so the kinetic energy of the ball at position 2 is

${ \sf {K_2 = \dfrac{1}{2} mv^{2} = 250J \: \: \: ......(2)}}$

Work done by gravity

${ \sf {W_{g.1→ 2} = mgh = 1000J \: \: \: \: ......(3)}}$

Denoting the work done by the air resistance as W$\sf _{R.1 → 2}$ and making use of eq (1),(2) and (3) in work kinetic.

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