Question

Q1) Please provide brief answers to the following question. Approximately one paragraph for each part ought to be sufficient.

(a) According to Newton's third law, when you push on a shopping trolley in the supermarket, the trolley pushes back on you with an equal and opposite force. Explain why it is that you can cause the trolley to move by pushing it, even though these forces are equal and opposite. Your explanation should refer to Newton's laws and all of the forces involved.

(b) The free-fall acceleration due to gravity on the Moon is about one-sixth of the free-fall acceleration on Earth. Think about trying to throw a ball with the fastest possible initial speed you are able to achieve. If you tried this first on the Moon, then on Earth, would you expect the ball's speed at the instant it left your hand on the Moon to be greater, less than or equal to its speed on Earth? Explain.

Answer 1

(a) Person force on trolley and trolley force on person is equal in magnitude but opposite in direction but the person has more mass than trolley and hence person has more inertia than trolley. This result net motion of trolley not of person.

(b) Velocity at time t is

where u is initial velocity of ball. Hence gravity has its effect on velocity of ball at time t not on initial velocity. Hence ball's speed at the instant it left person hand on the Moon is equal to its speed on Earth.

I will be glad to see your comment if you have any query and thumb up if you are satisfied. Thanks...