Question

chapter 07/ problem 055

A horse pulls a cart with a force of 21 lb at an angle of 13 degree above the horizontal a moves along at a speed of 5.2 mi/h. (a) How much work does the force do in 10 min? (b) What is the average power of the force?

Answer 1

Word done is given by

$W=\vec{F}.\vec{s}$

where F is force vector and s is displacement vector. So,

(a) in 10 minutes, work done by the force will be

$W=21cos13\degree\frac{5.2}{6} = 17.73\ lb^1mi^1$

(b) Average power would be

$P=\vec{F}.\vec{v}=21cos(13\degree)(5.2)=106.40\ lb^1mi^1 s^{-1}$

If you want your answers to be in SI units then you can convert them by using the fact that 1lb=0.453592 Kg and 1mi=1609.34 m

Hope this helps.