21. A toy cannon is fixed to a small cart and both move to the right with speed v along a straight track, as shown above. The cannon points in the direction of motion. When the cannon fires a projectile the cart and cannon are brought to rest. If M is the mass of the cart and cannon combined without the projectile, and m is the mass of the projectile, what is the speed of the projectile relative to the ground immediately after it is fired? AP Physics C: Mechanics Page 13 of 22 Scoring Guide Unit 4.3 Conservation of Momentum and Collisions (A) (B) (C) (D) (M) (E) (M -m) 22. A railroad car of mass 1500 kg rolls to the right at 4 m/'s and collides with another railroad car of mass 3000 kg that is rolling to the left at 3 m/s. The cars stick together. Their speed immediately after the collision is (A) = m's (B) 1 m's (0) $ m's (D) - m/'s (E) 7 m's23. m An object of mass m is moving with speed vo to the right on a horizontal frictionless surface, as shown above, when it explodes into two pieces. Subsequently, one piece of mass i'm moves with a speed - to the left. The speed of the other piece of the object is (B) (C) TED (D) 2 (E) 2vo24. X 3 m/s 2 m/s 2 m/s 3 m/s Before Collision After Collision Object X of mass mm is moving to the right with a speed of 3 m/s when it collides with object Y of mass m that is moving to the right with a speed of 2 m's, as shown above. After the collision, X is moving to the right with a speed of 2 m's and Y is moving to the right with a speed of 3 m/s. Which of the following is true of the collision? (A) It is elastic because momentum is conserved. B) It is elastic because kinetic energy is conserved. (C) It is inelastic because momentum is not conserved. (D) It is inelastic because kinetic energy is not conserved. (E) More information is needed to determine whether the collision is elastic or inelastic. 25. A toy spacecraft is launched directly upward. When the toy reaches its highest point, a spring is released and the toy splits into two parts with masses of 0.02 kg and 0.08 kg, respectively. Immediately after the separation, the 0.02 kg part moves horizontally due cast. Air resistance is negligible. True statements about the 0.08 kg part include which of the following? I. It could move north immediately after the spring is released. II. It takes longer to reach the ground than does the 0.02 kg part. III. It strikes the ground farther from the launch point than does the 0.02 kg part. (A) None B) I only (C) III only (D) I and II only (E) II and III only26. 2m Top View Two balls with masses m and 2m approach each other with equal speeds v on a horizontal frictionless table, as shown in the top view above. Which of the following shows possible velocities of the balls for a time soon after the balls collide?\f27. Two people are initially standing still on frictionless ice. They push on each other so that one person, of mass 120 kg, moves to the left at 2 m/'s, while the other person, of mass 80 kg, moves to the right at 3 m/'s. What is the velocity of their center of mass? (A) Zero (B) 0.5 m's to the left (C) 1 m's to the right (D) 2.4 m/'s to the left (E) 2.5 m's to the right