Problem 5 Train Reaction + Boat Run Three train cars are connected and moving at a speed up. A fourth car with speed 400 catches the group and connects to them, to make a group of four. (a) If each train car has identical mass, what is the speed of the group after the collision? (b) Now suppose the group (of four) collides with a fifth identical train car that was moving towards them with speed. If they all couple together, what is the final speed of the five car group? Andres (with mass m) is standing on the right side of a boat (with mass 3m) and decides to run as fast as he can to the other side. Lovleen is watching from the shore and notices he appears to be running with speed vo. There is no friction between the boat and water. (c) How fast is the boat moving? (d) How fast would Andres argue that he can run?

Must the total energy of a system be conserved whenever its momentum is conserved? Explain why or why not.

You friend claims that momentum is mass multiplied by velocity, so things with more mass have more momentum. Do you agree? Explain.

A 44.0-kg child finds himself trapped on the surface of a frozen lake, 10.0 m from the shore. The child slips with each step on the frictionless ice and remains the same distance from the shoreline. Egged on by his parents, he throws a 0.750-kg ball he is carrying toward the center of the lake with a horizontal speed of 1.50 m/s, in the direction opposite that of the shoreline. a. Does the act of throwing the ball cause the child to move? If so, what are the speed and the direction of his motion with respect to the Earth? b. What are the forces acting on the child when he throws the ball?

An object that has a small mass and an object that has a large mass have the same kinetic energy. Which mass has the largest momentum?

A car of mass 2000 kg is moving with a constant velocity of 10 m/s due east. What is the momentum of the car?

A rocket in deep space (zero gravity) accelerates by firing hot gas out of its thrusters. Does the rocket constitute a closed system? Explain.

A driver applies the brakes and reduces the speed of her car by 20 , without changing the direction in which the car is moving. By how much does the car’s momentum change?

A family is skating. The father (75 kg) skates at 8.2 m/s and collides and sticks to the mother (50 kg), who was initially moving at 3.3 m/s and at 45 with respect to the father’s velocity. The pair then collides with their daughter (30 kg), who was stationary, and the three slide off together. What is their final velocity?

A ball of clay of mass m is thrown with a speed v against a brick wall. The clay sticks to the wall and stops. Is the principle of conservation of momentum violated in this example?