QUIZ 4 

Exercises
and Problems from Conceptual Physics: Note that answers to odd numbered
problems are listed in the paperback supplement "Practicing
Physics." 

Ch
8 
exercises 
3 
4 
5 
18 
30 
31 
42 
47 








problems 

2 
3 
PLUG AND CHUG 
1 
3 
4 
5 







Ch
9 
exercises 
3 
4 
11 
12 
14 
19 
25 
28 
37 
47 
51 



problems 
1 
2 
3 
5 
6 
PLUG AND CHUG 
1 
2 







Hints:
HINTS WILL BE POSTED SOON….. CHECK BACK LATER!!! 



exercises


4. Sue's . See fig. 8.1  
5. varying linear speed. See fig. 8.1  
30. The weight of the beam acts at the geometric center of the beam. The torque of the boy = the torque due to the beam weight : (lever arm of boy) x (weight of boy) = (lever arm of beam weight) x (beam weight.).. The boy places the pivot at a location so that the above equation is true. Note that the lever arm of boy = distance between the pivot and the boy ....Note also that the lever arm of beam = distance between the center of the beam and the pivot.  
31. At the center of the earth. This is like the center of mass of a ring being at the geometric center of the ring.  
problems 

2. (a) torque = lever arm x force (b) set (0.25 m) x ( 80 N) = (0.10 m) x ( new force) . Find the new force.  
#4 AND #5 PLUG AND CHUG DISCUSSION AND HELPERS.
See page 141.
AS AN
INTERESTING MENTAL PROJECT TRY THIS to find compare the angular momentum of
the Earth orbiting the Sun compared to the angular momentum of the
Moon orbiting the Earth. Use
the formula for angular momentum = mvr.
Find the ratio of (mvr for the earth around the sun) to (mvr for the
moon around the earth.) ie. find ( mvr for the earth around the sun)/(mvr for
the moon around the earth.)...Use the Physical Data Table at the back of the
book or internet. Note: v = radius x angular speed, where angular speed = 6.28/(time for the
orbit) Background Actual Picture 



exercises 

4. force is the same if they have the same mass: force = mg. 

11. Nearer the moon because the moon has the smaller mass.  
14. The same from Newton's Third Law.  
19. Your weight would go down if the earth expanded. Your weight would up of the earth shrunk. See the formula in problem 3 below. d = distance from the surface to the center of the earth. If d increases, then mg decreases.  
28. There is a force of gravity on the pencil due to the earth. But you are falling with the pencil, so the pencil hovers.  
problems 

5. mg = GMm/d^{2 }, where d = 2x 10^{5} m + earth radius . Find g.  
6.
ma = GMm/d^{2 } . What would you cancel out? . 



