Rankers Physics

Work Energy Theorem: Practice Problem & Solution

A 5 kg ball when falls through a height of 20 m acquires a speed of 10 m/s. Find the work done by air resistance
500 J
-500 J
-750 J
+ 750 J

Short Solution (Best for NEET):

To solve this problem, we apply the core principles of Work Energy Theorem. Understanding the underlying formula is key to arriving at the correct answer below:

From work energy theorem, work done by all the forces is equal to change in kinetic energy.

So, Work done by gravity + Work done by air resistance = Final Kinetic Energy - Initial Kinetic Energy

5×10×20 + Work done by air resistance = 1/2× 5 ×(10²-0)

⇒ 1000 + Work done by air resistance = 250

⇒ Work done by air resistance = 250 -1000= -750 J

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