Summary

• Kinetic and potential energy
• Conservation of mechanical energy
• Energy diagrams

• Written Quiz Ch. 6




• Nonconservative forces
• work done by external forces
Example #1
Example #2
Example #3
Example #4
Example #5






• Power
• work/time
• Watts & horsepower
• instantaneous power
• P = F·v
Example #6

klm
A 3.00-kg textbook is given and initial speed of 2.00 m/s as it slides across a horizontal surface. The textbook slides to rest in a distance of 1.00 m. Calculate the coefficient of friction μ_k.
A. 0.408
B. 0.204
C. 0.102
D. 0.0340

Answer



















sb5 8.32
A 2000-kg car coasts from rest down a 5.00 m driveway with a 20.0° incline. If the friction force is 4000 N, what is the speed of the car at the bottom?
A. 3.68 m/s
B. 0.782 m/s
C. 8.94 m/s
D. 21.1 m/s

Answer



















PoP5 7.24a
An 80.0-kg sky diver jumps out of a balloon at an altitude of 1000 m and opens the parachute at an altitude of 200 m. Assuming that the total resistive force on the diver is constant at 50.0 N with the parachute closed and constant at 3600 N with the parachute open, find the speed of the sky diver when he lands on the ground.
A. 0 m/s
B. 600 m/s
C. 68.4 m/s
D. 24.5 m/s
Answer



















Walker5e Example 8-16
A golfer badly misjudges a putt, sending the ball only one-quarter of the distance to the hole. The original putt gave the ball an initial speed of v_i. If the force of resistance due to the grass is constant, what initial speed is needed to get the ball to the hole from its original position?
A. 2v_i
B. 3v_i
C. 4v_i
D. 16v_i
Answer



















Walker4e Active Example 8-2
A 95.0-kg diver steps off a diving board and drops h = 3.00 m to the water surface. At some depth d below the surface the diver comes to rest. If the work done by the external force (from the water) is −5120 J, what is the depth d?
A. 1.17 m
B. 2.50 m
C. 3.00 m
D. 7.67 m
Answer



















SB5 7.44
If a horse can sustain 0.70 hp output for 2.0 hours, how many 70 kg bundles can she lift 8.0 m in that time?
A. 12
B. 23
C. 685
D. 5490
Answer







































answer

B. 0.204




















answer

A. 3.68 m/s




















answer

D. 24.5 m/s

The skydiver begins with 784 kJ of gravitational potential energy but 720 kJ is removed by the nonconservative (or external to the system) air drag force. Here is a representative bar chart:




















answer

A. 2v_i

The work done by the friction from the grass during the first putt is −½mv_i². Because work is fd, four times the distance means friction will do four times the work during the second putt. That, in turn, means the ball needs four times the kinetic energy to make it to the hole. A ball with twice the speed will have four times the kinetic energy, so we need only double the initial speed.




















answer

B. 2.50 m

The work done by the water removes the kinetic energy the diver gains by falling a distance h + d






















answer

C. 685