Homework 6: Chapter 6, Problems 1-17. READ PROBLEMS IN COURSE PACK!!! 1. Each foot acts on the earth with a force 350 N ; the earth acts on each foot with a force 350 N.

2. Draw the stack of six units with the bottom spring compressed by 30 cm in the box to the right.

3. The mass m of each unit is 7.5 kg with a weight 75 N.

4. Mass 1: Compression force on top    0  ; bottom   75 N
Mass 2: Compression force on top 75 N   ; bottom 150 N
Mass 3: Compression force on top 150 N ; bottom 225 N
Mass 4: Compression force on top 225 N ; bottom 300 N
Mass 5: Compression force on top 300 N ; bottom 375 N
Mass 6: Compression force on top 375 N ; bottom 450 N

Compression force in spring (#) is :
C1 = mg = 75 N; C2 = 2mg = 150 N; C3 =2mg = 225 N;
C4 = 4mg = 300 N ; C5 = 5mg = 375 N ; C6 = 6mg = 450 N

(Give symbolic, not numerical, answers for 5-10)

5. The weight W of the mass m is   mg   .

6. The forces acting on this mass (are or are not) balanced.

7. If m = 0 for this mass, the value of C2 would be C1

8. What is the relationship between the compressions C1, C2, and ? Relationship is C2=C1+W

Problems 9 &and10 ask you to draw vectors within the mass.

9. Force vector, magnitude C (up) = C1 is shown.

10. The net force vector, magnitude C (down) = C2

11. Three equal masses hang from the ceiling by strings as shown at the right. If the tension in the top string is T , what is the magnitude of the tension in the lowest string?

a) T/3 b) –T/3 c) –mg/3 d) T e) 3mg

 Three masses, m , 2m , and 3m , hang from the ceiling by strings as shown at the right (below).
12. Draw on the figure to the right the tension vectors generated at the ends of the three strings. Label them from the top as , , and . 

13. What is the magnitude of , the tension in the lowest string?
a) 2mg   b) 3mg   c) 4mg   d) 5mg   e) 6mg

14. What is the magnitude of , the tension in the middle string?a) 2mg   b) 3mg   c) 4mg   d) 5mg   e) 6mg

15. What is the magnitude of the net gravitational force acting on earth from these masses?a) zero   b) 3mg  c) 4mg   d) 5mg   e) 6mg

16. A mass, m = 15 kg , has a spring with compression force C1 = 300N acting on its top face. What is the compression force, C2, in the spring acting on the bottom face of the mass if it is in a stack sitting on the ground?
a) 50 N   b) 150 N   c) 250 N   d) 350 N   e) 450 N

17. A mass weighs 10,000 N on the planet Mongo (gMongo = 25N/kg). What is its weight on the Earth?

a) 250,000 N   b) 400 N   c) 2.5 N   d) 4000 N   e) 2500 N


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