# Physics question: Work done by gravitational force

• Nov 15th 2009, 12:42 PM
TGS
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.
• Nov 15th 2009, 01:11 PM
skeeter
Quote:

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.

$W = F \cdot d = mgd = (0.9 \, kg)(9.8 \, m/s^2)(4.5 \, m)$
• Nov 15th 2009, 01:21 PM
TGS
Yes.. that didn't work. That was the first formula I used.
• Nov 15th 2009, 01:29 PM
skeeter
Quote:

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

the equation is correct ...

what did you calculate?
• Nov 15th 2009, 01:39 PM
TGS
ugh.. i figured it out.

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