# Work and kinitic energy

1. Oct 11, 2006

### problem

a constant force of magnitude 10 N makes an angle of 150. (measured counterclockwise) with the direction of increasing x as the force ascts on the 2 kg object. how much work is done on the object by the force as the object moves from the origin to the point with position vector. (2m)i - (4m)j?

what did till now is w = f x d and force was equal to 10Cos 150 x (-4.47)
i used the pathoagorious theomrem and got the value -4.47. 2^2 + 4^2 and then found the root for that answer. but stil my answer is wrong. Could someone please explain me what i am doing wrong. Thanks a lot for the help.

2. Oct 11, 2006

$$W = \vec{F}\cdot \vec{\Delta r} = (10 \cos(150) \vec{i}+10 \sin(150) \vec{j})\cdot(2\vec{i}-4\vec{j})$$.