[keh]

A man is doing push-ups. He has a mass of 68 kg and his center of gravity is located at a horizontal distance of 0.70 m from his palms and 1.00 m from his feet. Find the forces exerted by the floor on his palms and feet.

[Clough]

These sites may help you to solve the problem by applying the correct foumula:

Center of mass - Wikipedia, the free encyclopedia

Center of Gravity

[Capuchin]

Sorry clough! THis question isn't really about center of gravity :)

The man is acting like a bar pivoting about his feet.

You need to use:

sum of clockwise moments = sum of anticlockwise moments.

and :

moment = force * perpendicular distance.

Also you need:

Total upward force = total downward force.

Without more information you can only work out the answer for when he is not moving. (ie when he is at the top or the bottom of the push-up)

That should do it easily, good luck!

[vrooje]

Capuchin, are you saying you can't just use the center of gravity to calculate the effective mass at his hands and feet, and then use Newton's third law? It seems like you should get the same answer... though granted I haven't worked through it both ways, nor have I done a problem like this in a while.

[Capuchin]

I guess that should work too. I just always liked moments, something elegant about it :)