- #1

physlexic

- 14

- 0

## Homework Statement

On my exam, I got this problem wrong, which I believed was incredibly easy, and I don't know why it's wrong..."A constant force of 25 N is applied as shown to a block which undergoes a displacement of 7.5 m to the right along a frictionless surface while the force acts. What is the work done by the force?"

## Homework Equations

W = F * S

## The Attempt at a Solution

There is a displacement to the right, while the force vector is to the left, therefore work is in the negative.

displacement (s) = 7.5 m

F = 25 N (cos 30 degrees)

I chose cosine because we are only concerned for the x direction...which is adjacent to the angle of 30 degrees...

therefore

W = F * s = [25 N (cos 30)] * [-7.5 m]

W = -162 J

However the answe was -94 J...and this is because sine was used instead. Why? My professor didn't care to explain why...