Notes
$$W=Fd\cos\theta$$
- Work is positive if force and displacement point the same way; negative if opposite.
- Work-energy theorem: $W_{net}=\Delta K$.
Practice
You push a box 5 m with 10 N in the direction it moves. Work:
$10\times5$.
Friction on a sliding box does:
Opposes motion.
A force perpendicular to displacement (like the normal force on flat ground) does:
$\cos90°=0$.
$F(x)=3x^2$ N from $x=0$ to $x=2$ m. Work done:
$\displaystyle \int_0^2 3x^2dx=x^3\big|_0^2$.
Ready for more? Take the Unit 3 test.