Question

A fulcrum is placed under the center of a uniform 4.00m long, 3.00kg board. Child A has a mass of 42 kg. This child sits on the left end of the board; Child B has a mass of 26kg. Child B sits on the right end of the board. Where should child C (mass 21 kg) sit in order to have the board remain horizontal? What is the force of the fulcrum?

Answer 1

The torques:

m(A) •g•2 +(m/2) •g•1 =
=(m/2) •g•1+m(B) •g•2+m(C) •g•x

2{m(A)-m(B)}=m(C) •x
x=2(42-26)/21 = 1.52 (meters)