Answer
a) $W=4862.15lbf*ft=6.25Btu$
b) $W=1736.48lbf*ft=2.23Btu$
Work Step by Step
a) Considering the man and the cart and contents the total force will be:
$F=180lbf+100lbf=280lbf$
Then the work will be:
$W=FLsin(\theta)=(280lbf)*(100ft)*(sin(10^{\circ})=4862.15lbf*ft$
$4862.15lbf*ft*(\frac{1Btu}{778.17lbf*ft})=6.25Btu$
b) Considering just the cart and contents the total force will be:
$F=100lbf$
Then the work will be:
$W=FLsin(\theta)=(100lbf)*(100ft)*(sin(10^{\circ})=1736.48lbf*ft$
$1736.48lbf*ft*(\frac{1Btu}{778.17lbf*ft})=2.23Btu$
