Question

Check all the boxes that correspond to forces doing zero work

gravity acting on a projectile that has been launched straight up
You pushing your stalled car, but it doesn't budge
Drag acting on a plane flying horizontally
gravity acting on your car as it drives horizontally
An olympic weightlifter holding a barbell above their head (the barbell is motionless)
sliding friciton acting on a car slilding to a stop

Answer 1

The definition of work is force acting thru a distance: W = F * S

Forces doing zero work:

1) Pushing a stalled car that doesn't move

2) No work is done by gravity on car driving horizontally

3) No work is done on a motionless barbell