## Phys 100: Problem Set Week 8

These problems are due Wednesday October 31.

We finish Giancoli Chapters 6, focus on Chapter 7 (momentum), and start on chapter 8 (rotation) at the end of the next week

### Problems: These are due Wednesday, October 31 at the beginning of class

(1) Ch 5 P 88 - massing galaxies

(2) Ch 6 P 48

(3) Please omit Ch 6 P 5 - Done before! (Week 7 number 3)

(4) Ch 6 P 58

(5) Ch 6 P 62

(6) Ch 6 P 72

(7) A block sliding with mass 2.0 kg slides across a horizontal surface. The coefficient of kinetic friction is 0.35. The block collides with a horizontal spring, which compresses 50.0 cm before coming momentarily to rest. (a) If the spring constant is 50.0 N/m then, what is the speed of the block when it hits the spring? (b) How far past this point does the block slide before coming to rest again? Assume the coefficient of static friction is also equal to 0.35.

(8) Ch 7 P 4

(9) Ch 7 P 29

(10) Ch 7 P 35

(11) Ch 7 P 37

(12) Ch 7 P 42

(13) Ch 7 P 76

(14) The annnual total energy consumption in the Unitied States is about 9.76 X 10^(19) J [2004 data from the International Atomic Energy Agency (IAEA)]. (a) What is the average rate of consumption in Watts? (b) If the population is 312 million, what is the average rate electrical consumption per person? What is the average energy consumed per person in a year? (c) Sunlight transfers approximately 1.0 kW per square meter by radiation (or, what we call "sunlight"). If this energy could be collected at an efficiency of 40%, how large an area would be required to collect the energy used by the US? Compare area this to the area of your home state. (Currently the most efficient solar arrays have an efficiency of 20%.) (d) The data for Ireland is 5.99 X 10^(17) J with a population of 4 million. What is the average annual energy consumed per person? How large an area would be required? Compare these numbers with the ones for the USA.