Center of Mass

[buffgilville]

A man of mass 83.8 kg stands on top of a uniform ladder whose mass is 11 kg and whose length is 8.7 meters. Find the distance (in meters) from the base of the ladder to the center of mass.

Here's what I did:
X(center of mass) = (83.8*8.7) + (11*0) / (83.8+11)
= 7.69meters

but the correct answer is 8.20meters. What did I do wrong? Please help. Thanks!

[ehild]

A man of mass 83.8 kg stands on top of a uniform ladder whose mass is 11 kg and whose length is 8.7 meters. Find the distance (in meters) from the base of the ladder to the center of mass.

Here's what I did:
X(center of mass) = (83.8*8.7) + (11*0) / (83.8+11)
= 7.69meters

but the correct answer is 8.20meters. What did I do wrong? Please help. Thanks!


You should consider the ladder as if its mass would be concentrated at its own centre of mass, that is at 8.7/2=4.35 m height.

ehild