When the formula for
work works
W = Fd cosθ only works
when the Force does
not change as the object
moves.- A 15 kg crate is moved along a horizontal floor by a warehouse
worker who’s pulling on it with a rope that makes a 60° angle with
the horizontal. The tension in the rope is 200 N and the crate slides
a distance of 10 m. How much work is done on the crate by the
worker?
Here’s How to Crack It
The figure below shows that FT and d are not parallel. It’s only the component of
the force acting along the direction of motion, FT cosθ, that does any work.
Therefore
W = (FT cos θ)d = (200 N • cos 60°)(10 m) = 1,000 J- In question 2, assume that the coefficient of kinetic friction
between the crate and the floor is 0.4.