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Lakhmir Singh Solutions Class 9 Physics Solutions for Exercise in Chapter 4 - Work And Energy

Question 30 Exercise

A ball of mass 200g falls from a height of 5 meters. What is its kinetic energy when it just reaches the ground?

Answer:

Mass = 200 g = 0.2kg

Height = 5m

Initial velocity, u = 0

Acceleration due to gravity, g = 9.8 m/s2

Final velocity, v

Using the third equation of motion,

v^2-u^{2\ }=2gs^{ }

v^2 = 98

Kinetic energy = \frac{1}{2}mv^2

Kinetic energy = (½)(0.2)(98) = 9.8J

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