Some nearly equivalent problems in the text:
C-6.5, 6.11, 6.15;
P-6.1, 6.7, 6.9, 6.24, 6.25, 6.28, 6.30, 6.38, 6.40, 6.47
Conceptual Questions:
1. Give some examples of nonconservative force. (C-6.8)
2. Which is the form of energy associated with an object's motion? (C-6.11)
3. Which is the form of energy associated with an object's location in a conservative force field? (C-6.11)
4. The unit of work, Joule, is dimensionally the same as:
a. Newton/second
b. Newton/kilogram
c. Newton*second
d. Newton*meter
5. The unit of power, Watt, is dimensionally the same as:
a. Joule*second
b. Joule/second
c. Joule*meter
d. Joule/meter
6. Work done on a system puts energy into it. Work done by a system takes energy out. Give examples of each. (C-6.5)
7. A weight is connected to a spring suspended from the ceiling. If it is pulled downward and released, it will oscillate up and down. Describe the forms of energy present at different points in the oscillation. Is energy conserved? (C-6.15)
Numerical Problems:
Try to answer these questions by energy considerations, not by applying
"linear motion with constant acceleration".
1. A very light cart holding a 300 N box is moved at constant velocity across a 15 m level surface. What is the net work done in the process? (P-6.7)
2. A 7 kg bowling ball falls from a 2.0 m shelf. Just before hitting the floor, what will be its kinetic energy (g = 9.8 m/s2 and assume air resistance is negligible)? (P-6.25)
ans: 137 J
3. An rock is thrown straight up with an initial velocity of 15 m/s. Ignore energy lost to air friction. How high will the rock rise? (P-6.30)
4. A 20 N crate starting at rest slides down a rough ramp 5.0 m long, inclined at 25ø with the horizontal. 20 J of energy is lost to friction. What will be the velocity of the crate at the bottom of the incline? (P-6.28)
5. Rupel pushes a box 5 m by applying a 25 N horizontal force. What work does she do? (P-6.1)
ans: 125 J
6. What is the kinetic energy of a 0.135 kg baseball thrown at 40 m/s (90 mph)? (P-6.9)
ans: 108 J
7. A 2000 kg ore car rolls 50 meters down a frictionless 10ø incline. If there is a horizontal spring at the end of the incline, what spring constant is required to stop the ore car in a distance of 1 meter? (P-6.24)
8. A 60 kg woman runs up a flight of stairs having a rise of 4 meters in a time of 4.2 seconds. What average power did she supply? Neglect friction. (P-6.47)
ans: 560 W
9. An automobile delivers 30 hp to its wheels when moving at a constant speed of 22 m/s. What is the resistance force on the automobile at this speed (1 hp = 746 Watts)? (P-6.38)
ans: 1,020 N
10. A girl and her bicycle have a total mass of 40 kg. At the top of the hill her speed is 5 m/s. The hill is 10 m high and 100 m long. If the force of friction as she rides down the hill is 20 N, what is her speed at the bottom? (P-6.28)
ans: 10 m/s
11. Water flows over a section of Niagara Falls at a rate of 1.2 x106 kg/s and falls 50 m. What is the power generated by the waterfall?
ans: 588 MW (P-6.40)