∑ 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