Download CHAPTER 8 TEST

Chapter 7 Review
7.1. Work: The Scientific Definition
• Explain how an object must be displaced for a force on it to do work.
• Explain how relative directions of force and displacement determine whether the work done
is positive, negative, or zero.
• Calculate the work done by a force on an object given the force and displacement.
7.2. Kinetic Energy and the Work-Energy Theorem
• Explain work as a transfer of energy and net work as the work done by the net force.
• Explain and apply the work-energy theorem.
7.3. Gravitational Potential Energy
• Explain gravitational potential energy in terms of work done against gravity.
• Show that the gravitational potential energy of an object of mass m at height h on Earth is
given by PEg = mgh .
• Show how the work-energy theorem explains the conversion between gravitational potential
energy and kinetic energy for an object moving under the influence of gravity.
• Show how knowledge of the potential energy as a function of position can be used to simplify
calculations and explain physical phenomena.
7.4. Conservative Forces and Potential Energy
• Define conservative force, potential energy, and mechanical energy.
• Explain the potential energy of a spring in terms of its compression when Hooke’s law applies.
• Use the work-energy theorem to show how having only conservative forces implies
conservation of mechanical energy.
• Apply conservation of mechanical energy to solve mechanics problems in terms of potential
energies instead of forces.
7.5. Nonconservative Forces
• Define nonconservative forces and explain how they affect mechanical energy.
• Show how the principle of conservation of energy can be applied by treating the conservative
forces in terms of their potential energies and any nonconservative forces in terms of the
work they do.
7.6. Conservation of Energy
• Explain the law of the conservation of energy.
• Express conservation of energy in equation form.
• Describe some of the many forms of energy.
• Summarize an effective problem-solving strategy for applying conservation of energy.
• Examine commonly encountered examples of transformations between forms of energy.
• Define efficiency of an energy conversion process as the fraction left as useful energy or
work, rather than being transformed, for example, into thermal energy.
7.7. Power
• Define power as the rate of doing work and identify typical examples of power.
• Calculate power by calculating changes in energy over time.
• Examine power consumption and calculations of the cost of energy consumed.
Equations:
Work
W = Fd cos 
Kinetic Energy
K (=KE) = ½ mv2
Potential Energy
Ug (= PEg) = mgh
Thermal Energy
Q = Ffd = FNd
Q = mgd
Q = mgcos  d
Work-Energy Theorem
No change in height:
Change in height:
Uspring = ½ kx2
(horizontal surface)
(ramp)
W = K
(no friction)
W = K + U (no friction)
W = K + Q
W = K + U + Q
Conservation of Mechanical Energy
Ki + Ui = Kf + Uf
(no friction)
Ki + Ui = Kf + Uf + Q
(with friction)
Force
Fg = mg
Fspring = kx
Review Chapter 7 Section Summary
Practice
7.1. Work: The Scientific Definition
A. How much work is done when you push on an object and it does not move?
B. F = 10 N, d = 5.0 m and  = 0o. Find work.
C. F = 20 N, d = 3.0 m and  = 60o. Find work.
D. F = 5.0 N, d = 7.0 m and  = 180o. Find work.
(friction)
(friction)
7.2. Kinetic Energy and the Work-Energy Theorem
A. W = 8.0 J, m = 4.0 kg, vi = 0 m/s. Find vf.
B. W = 24 J, m = 4.0 kg, vi = 0 m/s, vf = 3.0 m/s. Find Q
7.3. Gravitational Potential Energy
A. m = 5.0 kg, h = 2.0 m. Find W.
B. m = 5.0 kg, h = 2.0 m. Find Ug.
C. hi = 4.0 m, hf = 0 m, vi = 0 m/s. Find vf.
D. hi = 4.0 m, hf = 0 m, vi = 6.0 m/s. Find vf.
E. hi = 10.0 m, hf = 3.00 m, vi = 0 m/s. Find vf.
7.4. Conservative Forces and Potential Energy
A. F = 75 N, x = 3.0 m. Find k.
B. k = 30 N/m, x = 2.0 m. Find Us.
7.5. Nonconservative Forces
A. Ff = 4.0 N, d = 5.0 m. Find Q.
B.  = 0.200, m = 2.0 kg, d = 3.0 m. Find Q on the flat surface.
C.  = 0.200, m = 2.0 kg, d = 3.0 m,  = 60o. Find Q on ramp.
D. m = 10 kg, d = 4.0 m, Q = 156.8 J. Find .
E. In D. above, how much work was done to move the 10 kg object 4.0 m at a constant speed?
7.6. Conservation of Energy
A. A vertical spring is stretched and released. k = 150 N/m, x = 1.0 m, m = 1.0 kg. Find v max.
B. A vertical spring is stretched and released. k = 150 N/m, x = 1.0 m, m = 1.0 kg. Find h.
C. A moving block collides and compresses a spring on a frictionless surface. m = 2.0 kg, vi =
1.0 m/s, vf = 0, k = 32 N/m. Find xmax (= xf).
7.7. Power
A. W = 20 J, t = 2.0 s. Find P.
B. F = 30 N, d = 5.0 m, t = 3.0 s. Find P.
C. Cost = $0.13/kW h, P = 100 W, t = 6.0 h. Find $.
Solutions:
7.1 A. 0
B. 50 J
7.2 A. 2.0 m/s
B. 6.0 J
7.3 A. 98 J
B. 98 J
7.4 A. 25 N/m
B. 60 J
7.5 A. 20 J
C. 30 J
D. -35 J
C. 8.9 m/s
D. 11 m/s
E. 12 m/s
B. 12 J
C. 5.9 J
D. 0.40
E. 156.8 J
7.6 A. 12 m/s
B. 7.7 m
C. 0.25 m
7.7 A. 10 W
B. 50 W
C. $0.08