Dept. of Physics & Astronomy

Office: Watanabe Hall, Rm. 426, (808) 956-2922

E-mail: nassir @ hawaii.edu

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PHYS 151 Exam & Answers page*

**Part A**

**1a.** A (True)

**1b.** A (True)

**1c.** A (True)

**1d.** B (False)

**2.** E

**3.** A (the closer that the overall mass distribution is
located to the spin axis, the smaller the moment of inertia of
the object)

**4.** F

**5.** B and D (if moment of inertia is constant, then in order
for L to be decreasing, angular speed must also be decreasing)

**6a.** C

**6b.** F (if *R* of a sphere doubles, its mass increases
by 8x, so its entire moment of inertia increases by 32x)

**7a.** B

**7b.** E

**7c.** F

**7d.** G

**8.** B (want largest possible lever arm, and force as perpendicular
as possible to lever arm direction)

**Part B**

**1a.** 8.6 m/s (conservation of energy: KE of pair of cars
is converted to work done by friction force)

**1b.** 15 m/s = 34 mi/h (using conservation of momentum through
the collision)

**2.** 0.76 away from the fulcrum, on Bryce's side (find
position of Crystal so that total center-of-mass lies exactly
at fulcrum position; OR sum torques of all three children about
fulcrum/pivot and set equal to zero)

**3.** *F*_spring = 2.8 x 10^3 N