Figure shows a thin uniform rod `50 cm` long and has a mass of `100 g`. A hollow metal ball is filled with air and has a diameter `10 cm` and total mass `50 g` is fixed to one end of the rod. At what point along its length will the ball and rod balance horizontally?

Options

A. `20 cm` from the centre of the rod
B. `10 cm` from the centre of the rod
C. at the centre of the rod
D. where the ball is attached to the rod

Answer

B

Explanation

The rod will balance about centre of mass, so distance of centre of mass from the left end.
`x_(CM)=(m_(1)x_(1)+m_(2)x_(2))/(m_(1)+m_(2))=(100xx25+50xx55)/(100+50)=35cm`
Therefore, distance form centre of rod `=35-25=10cm` to the right