Shopping cart work Part A $|$ Problem

A shopper pushes a grocery cart $20\mathrm{.}0$ m at constant speed over a level floor, against a $35\mathrm{.}0$ N frictional force. His pushing force is directed at an angle of $25$ degrees below the horizontal. What is the change in thermal energy cause by the frictional force acting on the cart and the ground?

$01$

$500$ J

$5001$

$-634$ J

$7001$

$-7001$