Give a reason why mass of a body is constant everywhere.

When I look at the tyres of a moving vehicle in a movie the look as if they are moving in the opposite direction. How can we explain this phenomenon/effect?

A student wearing sharp pointed heeled shoes is likely to damage a soft wooden floor. Explain.

A ball ? is always in neutral equilibrium. Explain.

Suggest two methods of improving the efficiency of a machine.

Why is efficiency of a machine is always less than 100% ?

helicopter of mass 3000kg rises vertically at a constant speed of 25m/s if the acceleration due to gravity is10m/s2 ,determine the resultant force working on the helicopter