Which statement below is TRUE? a) In order to have angular momentum be conserved
ID: 1389862 • Letter: W
Question
Which statement below is TRUE?
a) In order to have angular momentum be conserved there must be no net external forces on the system involved
B) When quickly rotating bike wheel (with vertical axis of rotation) held by a person on a stationary stool is flipped by 180 degrees, the wheel exerts a torque on the rest of the system and the rest of the system exerts a torque back on the wheel. Due to the presence of these torques on the system (stool,person, and wheel), the system CANNOT have angular momentum conserved.
C) If two equal mass balls hit each other in a glancing inelastic collision, then the angle between the two ball's final velocities will always be 90 degrees.
D) For a dynamic Atwood's machine with a massive pully (see picture) the string on either side of the pully would have different tensions (assume massless string).
E) If now the atwood's machine has string with mass and hte hanging mass are moving, hte tension on the left side of hte pully would change over time and similarly for hte string on the right side.
F) Only D) and E) above are true
G) None of the answers A) through E) above are TRUE
Explanation / Answer
a) True. When there is no external force the torque acting on the system is zero. Therefore the net angular momentum will conserved.
T = dw / dt = 0 ==> w = constant
b) False. Angular momentum is conserved. Because initially the angular momentum is in upward direction when the table is flipped the direction of angular momentum is downward.
c) False. Because in inelastic collision two bodies will stick together.
d) True. The tension on either side will be same.
e) True. Then the tension will be changes on both sides with time.
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