18. A go-round spinning at a constant angular speed, person is standing near the

Question

18. A go-round spinning at a constant angular speed, person is standing near the center of a merry- o. He then speed when he gets to the edge, o? walks towards the edge of the ride. What can be said about the system's angular b. 19. An 8 gram mass moving at 7 m/s hits a 12 gram mass at rest in an elastic collision. What is the velocity of the 12 gram mass after the collision? a. 5.6 m/s b,-1.4m/s c. 1.4 m/s d. 8.4 m/s e. None of the above. , 12?0.2 0.2 2. 20. Two objects of mass m, and m2 stick together in a collision, which of the following statements is not true? a. This is a perfectly inelastic collision. b. The energy after the collision is less than before the collision. c. Final to initial kinetic energy ratio mi/(m +m) Both b and c Doubling either mass will double the system's total momentum. d. e. 21. Complete the following statement: A system's energy is conserved when a. there is an external force acting on it. b. the system does work on the environment. c. work is done on the system. d. the system is isolated. e. the system is in equilibrium. Test A: Page 6 of9

Explanation / Answer

18. Angular momentum (L = mrw 2) of the system is conserved. Initially all angular momentum is due to the merry go round. Later it is distributed with the peroson and the merry-go-round. So, Wi > Wr

19. From elastic collision,

v - u = 7

From energy conservation,

0.5*8*7*7 = 0.5*8*u*u + 0.5*12*v*v

96 = 2u*u + 3v*v

96 = 2(v-7)*(v-7) + 3v*v

192 = 5v*v - 28v

V = 48/5 = 9.6 m/s

20. (C) Final to initial kinetic energy is not M1/(M1+M2)

21. A system's energy is conserved when the system is isoaisol.

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