The  Work – Energy Theorem

∑ W= Δ Ek

Example

On an object act a force F of60 N and a frictional force of 20 N

The object goes to the right. The initial velocity is 4.0 m s-1

Calculate the velocity v2   at a displacement of 30 m (see drawing)

∑ W= E k,2  – E k,1

Fnet  s = ½ m v 22 – ½ m v12

(40 )( 30) = ½ (2.0)( v2)2 – ½ (2.0)( 4.0)2

1200 = v22 – 16

v22 = 1216

v2 = 34.9 m/s

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