1. The problem statement, all variables and given/known data In this problem, take g = 10 m s-2. A uniform plank of length 14 m long and mass 20 kg is being supported at B and C as shown above. Two boys X and Y of masses 20 kg and 50 kg respectively are right on top of the supports. X starts to walk towards A and Y walks towards D at the same time. If both boys walk at 1.0 m s-1, the plank begins to overturn after how many seconds? 2. Relevant equations Clockwise moment = anticlockwise moment fs=fs 3. The attempt at a solution The answer given is 4seconds. i can't work it out,really need help. Need a little hint please. Thanks.