Download Review: Momentum and Impulse, Conservation of Momentum

Physics Exam Review: Work, Energy & Power; Electrostatics, Electric Fields & Potential
Review: Energy, Work and Power
Definitions:
Work
Potential Energy
Kinetic energy
Work-Energy Theorem
Power
Law of Conservation of Energy
Machine
Mechanical Energy
Concepts:
Know that work is only done by the force in the direction of motion.
Know objects in motion have the ability to do work.
Know how PE and KE change in relation to height and movement.
Know how to solve mechanical advantage and efficiencies.
Review: Electrostatics
Definitions:
Ion
Conservation of charge
Conductors
Insulators
Polarization
Concepts:
Know properties of positive and negative charges.
Know properties of ions.
Know difference between conductors and insulators
Properties of a hollow conductor
Understand charge by contact (conduction) and charge by induction and the affects on neutral
and charged spheres.
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Physics Exam Review: Work, Energy & Power; Electrostatics, Electric Fields & Potential
Review: Electic Fields and Potential
Definitions:
Electric Field Strength
Electric Potential Difference
Concepts:
Know what electric potential energy is dependent on.
Know how work on a charge in an electric field affects PE.
Know how to draw electric field lines correctly.
Know what charge is used to test an electric field.
SI Units
1. Write the SI unit for each of the following: (6 points)
a) Work
e) PE
b) Power
f) Electric Field
c) KE
g) Electric Potential Difference
d) Charge
Equations: (provided on exam, but you should know how to use)
Work
W=Fd
W=qEd
Coulomb's Law
F = k q1 q2 / d2
(k = 9.0 x109 Nm2/C2)
Potential Energy
Ug = PE = m g h
Charges
qp = + 1.6 x10-19 C
qe = - 1.6 x10-19 C
Kinetic Energy
KE = 1/2 m v2
Power
P = W/t
Conservation of Energy
KEi + PEi = Kef + PEf
Voltage
V=Ed
V=W/q
Electric Field Strength
E=F/q
E = k q / d2
(k = 9x109 Nm2/C2)
Mechanical Advantage
MA = dInput / dOutput
MA = RampLength / RampHeight
MA = FOutput / FInput
Mechanical Efficiency
ME = actual MA / ideal MA
Force
F=ma
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Physics Exam Review: Work, Energy & Power; Electrostatics, Electric Fields & Potential
Word Problems
1. Clyde, a stubborn 3500 N mule, refuses to walk into the barn, so Farmer MacDonald must
drag him up a 5.0 m ramp to his stall, which stands 0.50 m above ground level.
a) What is the ideal mechanical advantage of the ramp?
b) If Farmer MacDonald needs to exert a 450 N force on the mule to drag him up the ramp with a
constant speed, what is the actual mechanical advantage of the ramp?
c) What is the efficiency of the ramp?
2. A construction worker uses a board and log as a lever to lift a heavy rock. If the input arm is
3 m long and the output arm is 0.75 m long, what is the MA of the lever?
3. A ramp with a mechanical advantage of 8 lifts objects to a height of 1.5 meters. How long is
the ramp?
4. A weightlifter raises a 180 kg barbell to a height of 1.95 m. How much work is done by the
weightlifter in lifting the barbell?
5. An elevator lifts a total mass of 1.1x103 kg a distance of 40.0 m in 12.5 s. How much power
does the elevator demonstrate?
6. What power does a pump need to lift 35 kg of water per minute from a depth of 110 m?
7. An atom with 7 total electrons has a net charge of - 3.2x10-19 C .
a. Does the atom have too many or too few electrons compared to normal (a neutral state)?
b. How many of these electrons make up the difference, producing the net charge?
(Hint: Use the value above.)
c. How many protons must the atom have?
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Physics Exam Review: Work, Energy & Power; Electrostatics, Electric Fields & Potential
8. Two identical metal balls carry charges of +3.00x10-6 and -6.00x10-6, respectively. Their
centers are 1.00 m apart.
a) Compute the size of the electrical force between them.
b) Was the force in part a) attractive or repulsive?
9. A negative charge of 2.0x10-8 C experiences a force of 0.060 N to the right in an electric
field. What are the field's magnitude and direction at that location? (Hint: electric field
direction is determined by placing a positive test charge in it)
10. What is the electric field strength and direction at a position that is 1.6 m east of a point
charge of + 7.2x10-6 C ?
11. A voltmeter reads 400 V across two charged, parallel plates that are 0.020 m apart. What is
the electric field between them?
12. The electric field in a particle-accelerator machine is 4.5x105 N/C. How much work is done
to move a proton 25 cm through the field? (Hint: qp = 1.60x10-19 C)
13. An oil drop weighs 1.9x10-15 N. It is suspended in an electric field of 6.0x103 N/C.
a) What is the charge on the drop? b) How many excess electrons does it carry?
(Hint: qe = - 1.60x10-19 C)
14. A bike rider approaches a hill at a speed of 8.5 m/s. The combined mass of the bike and
rider is 85.0 kg. a) Find the initial kinetic energy of the bike and rider. b) Ignore friction, at
what height will the bike come to rest?
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