E. Circular Motion II

**Homework**

** **

**8.1 Rigid Bodies and Rotations**

**5, 10, 13**

10: v_{cm }=
rw solve for w

13: a = a_{t}/r solve for a. Next, w^{2} = w_{o}^{2}
+ 2aq where you solve for q

** **

**8.2 Torque,
Equilibrium, Stability**

**14, 18, 19, 24, 30, 31**

** **

14: Look at figure 8.5 c on p. 256 and you’ll see SF = 0 but the St doesn’t = 0

18: When the force
is applied ^
to the length of the wrench, minimum force is required and the lever arm equals
the length of the wrench. At q = 90^{o},
r_{^}=
0.15 m

t = Fr_{^}
solve for F

19: In this case, r_{^}
= 0.15 sin 30. Use formula from 18 and
again solve for F.

24: St = 0. Don’t forget that to find distances you must subtract from the designated pivot point.

30: see example 8.5 on p. 259

31: Choose where the string acts as the axis and work from the bottom up. Realize that St must = 0 since they aren’t rotating.

**Even Answers:**

10: 1.7 rad/s

14: b

18: 1.7 x 10^{2}
N

24: a: 83.3 cm b. 62.5 g

30: 2.1 x 10^{2}
N