Momentum Help: Solving a Child's Physics Problem

[psychfan29]

Momentum- HELP!

A 40kg child stands at one end of a 70kg boat that is 4m in length. The boat is initially 3m from the pier. The child notices a turtle on a rock at the far end of the boat and proceeds to walk to that end to catch the turtle. Neglecting friction between the boat and the water
a) Describe the susequent motion of the system (child+boat).
b) Where will the child be relative to the pier when he reaches the far end of the boat?
c) Will he catch the turtle? (Assume he can reach out 1m from the end of the boat.)

I don't really know how to do any of this. I don't even know where to start. Please help!

 

[robertm]

The key to this situation is that friction is negated. What would happen if you tried to walk forward on ground that has no friction? How do your feet make you move forward? Try and see the situation from a outside reference point. What would the boy look while walking if you were watching from the dock?

 

[Moetasim]

Hello,

I understand that you are struggling with solving this physics problem. Let me provide some guidance to help you understand and solve it.

First, let's define some important concepts in this problem. Momentum is the product of an object's mass and velocity, and it is a measure of how much motion an object has. In this problem, we have a system consisting of a child and a boat, and we need to consider the momentum of both objects.

a) To describe the subsequent motion of the system, we need to apply the law of conservation of momentum. This law states that the total momentum of a closed system remains constant unless acted upon by an external force. In this case, the system is initially at rest, so the total momentum is zero. As the child moves to the other end of the boat, their momentum increases while the boat's momentum decreases to keep the total momentum at zero. This results in the boat moving in the opposite direction with a lower velocity. The child and the boat will continue to move in opposite directions until they reach a point where their momenta are equal, and the system comes to a stop. This is known as the center of mass of the system.

b) When the child reaches the far end of the boat, they will be at the center of mass of the system, which is 2m from the pier. This means that the child will be 2m away from the pier when they reach the far end of the boat.

c) It is difficult to determine if the child will catch the turtle without knowing the initial position of the turtle. However, we can calculate the distance the turtle needs to be from the pier for the child to catch it. Since the child can reach out 1m from the end of the boat, the turtle needs to be within 1m of the pier for the child to catch it. This means that if the turtle is more than 1m away from the pier, the child will not be able to catch it.

I hope this helps you understand and solve the problem. Remember to always start by defining the important concepts and applying relevant laws and equations. If you still have trouble solving it, I suggest seeking help from a teacher or tutor. Good luck!