Presenting ‘Ball of Mystery’

Number of ball and socket joints present in human body is

How does hierarchial system of classification help the scientist to unravel the mystery of living world?

Out of 4 identical balls of radius r, 3 balls are placed on a plane such that each ball touches the other two balls.The 4^(th) ball is placed on them such that this ball touches all the three balls. What is the distance of centre of 4^(th) ball from the plane?

A solid shperical ball of mass m and radius R is present on a rough horizontal surface. A person hit the ball at distance h above the centre of the ball as shown in the figure. Find out the h such that the ball starts pure rolling just after impact.