A box of mass 8.0 kg rests on a horizontal rough surface. A string attached to the box passes over a smooth pulley and supports a 2.0 kg mass at its other end.
When the box is released, a frictional force of 6.0 N acts on it.

What is the acceleration of the box?

What is the definition of the force on a body?

Newton’s third law of motion is often summarised as ‘Every action (force) has an equal and opposite reaction.’
A book rests on a table.

If the weight of the book is the ‘action’ force, what is the ‘reaction’ force?

Water is pumped through a hose-pipe at a rate of 90 kg per minute. It emerges from the hose-pipe horizontally with a speed of 20 m s^–1.

Which force is required from a person holding the hose-pipe to prevent it moving backwards?

A man weighs 240 N on Mars where the acceleration of free fall g is 4 m.s^–2. On the Moon, g is 2.0 m.s^-2.

Which statement is correct?