# Homework Assignment #4

Due:
Wednesday 5 March (Sections 001 and 801) (Note different quiz day!)
Thursday 6 March (Sections 002 and 802)

Chapters 7 and 8.

### QUESTIONS

Chapter 7 - 1, 5, 6, 7, 11, 15.
Chapter 8 - 1, 2, 3, 12.

### PROBLEMS

Chapter 7 - 3, 6, 17, 24, 32, 36, 43, 44, 50, 51, 58.
Chapter 8 - 4, 6, 10, 11, 16, 20A, 20, 25A, 25, 30, 35, 57.

Q 7-1) The displacement ds is perpendicular to the force F.
Q 7-5) No.
Q 7-7) The speed is unchanged (the direction of velocity might change).
Q 7-11) The more massive bullet has twice the kinetic energy of the smaller mass bullet.
Q 7-15) Pushing on a wall: ds=0. No displacement, no work.
Tension in a string that keeps a particle in uniform circular motion: F is perdendicualr to ds, no work.
Q 8-1) If all the forces on the ball were conservative, the ball would swing back exactly to the point from which it was released. However, air resistance is non-conservative and it happens to decrease, not increase, the total mechanical energy. The ball will swing back to a lower height.
Q 8-2) Yes.
Q 8-3) They will NOT agree on the VALUE of the potential energy, but they will agree on the CHANGE in potential energy and on the kinetic energy.
Q 8-12) K is a maximum at launch and just before hitting the ground. U is a maximum at the highest point in the arc.
P 7-3)
1. 31.9 J
2. 0 J
3. 0 J
4. 31.9 J

P 7-6)
1. 294,000 J
2. 294,000 J

P 7-17)
1. 16.0 J
2. 36.9o

P 7-24)
1. 24.0 J
2. -3.00 J
3. 21.0 J

P 7-32)
1. 1.20 J
2. 5.00 m/s
3. 6.30 J

P 7-36)
1. 60.0 J
2. 60.0 J

P 7-43) 1.25 m/s
P 7-44)
1. 0.791 m/s to the left
2. 0.531 m/s to the left

P 7-50) 234J
P 7-51)
1. 63.9 J
2. -35.3 J
3. -9.5 J
4. 19.1 J

P 7-58) 830 N
P 8-4)
1. Ax2/2 - B3/3
2. change in U = 5A/2 - 19B/3
change in K = -5A/2 + 19B/3 = -(change in U)

P 8-6)
1. 80.0 J
2. -80.0 J
3. 6.32 m/s

P 8-10) 2.94 m/s
P 8-11) v = sqrt(3 g R)
N = 0.098 newtons downward
P 8-16)
1. v = sqrt(vo2 + 2gR + 2gR cos theta)
2. sqrt(gR)
3. No.

P 8-20A)
P 8-20) 1.96 m
P 8-25A)
P 8-25) 3.74 m/s
P 8-30) 0.344 m
P 8-35) 0.327
P 8-57)

Please report any corrections to Professor Scalise.