Question

Rod of length 80 cm and mass3.2kg hp supported horizontally by the two spiring balances C and D .Balance C is 20cm from one end while D 30cm on the other.Find reading of each balance.

Answer 1

This one's probably about moments. If would be helpful to draw a diagram to visualize the respective forces acting on the rod. (so you would have balances C and D at each end of the rod, exerting an upward force on the rod. The weight of the rod exerts a downward force on the middle of the rod)

To examine the reading on each balance, take the other balance as a pivot.

Moment = Force x Distance from pivot

For example, if we want to find the reading on Balance D, Balance C is the pivot. 2 forces are acting on the rod - it's weight, and the upward countering force exerted by Balance D. Since the rod is assumed to be in equilibrium,

the moments exerted by both forces are the same:

Weight x Distance from pivot = Balance D x Distance from pivot

The distances from the pivot of the respective forces should be easy to calculate with a diagram.

Then repeat the same with balance D