# Thread: Physics question: Work done by gravitational force

1. ## Physics question: Work done by gravitational force

A ball of mass 0.9 kg falls downward, as shown in the diagram above. Initially you observe it to be 4.5 m above the ground. After a short time it is just about to hit the ground.
During this interval how much work was done on the ball by the gravitational force?

I've tried using Mass * 9.8 N/kg * 4.5 m

but that didn't work.

2. Originally Posted by TGS
A ball of mass 0.9 kg falls downward, as shown in the diagram above. Initially you observe it to be 4.5 m above the ground. After a short time it is just about to hit the ground.
During this interval how much work was done on the ball by the gravitational force?

I've tried using Mass * 9.8 N/kg * 4.5 m

but that didn't work.
$\displaystyle W = F \cdot d = mgd = (0.9 \, kg)(9.8 \, m/s^2)(4.5 \, m)$

3. Yes.. that didn't work. That was the first formula I used.

4. Originally Posted by TGS
Yes.. that didn't work. That was the first formula I used.
the equation is correct ...

what did you calculate?

5. ugh.. i figured it out.

I obviously can't read properly because I entered in 36.69J instead of 39.69J.