Ch 07: Work & EnergySee all chapters
All Chapters
Ch 01: Units & Vectors
Ch 02: 1D Motion (Kinematics)
Ch 03: 2D Motion (Projectile Motion)
Ch 04: Intro to Forces (Dynamics)
Ch 05: Friction, Inclines, Systems
Ch 06: Centripetal Forces & Gravitation
Ch 07: Work & Energy
Ch 08: Conservation of Energy
Ch 09: Momentum & Impulse
Ch 10: Rotational Kinematics
Ch 11: Rotational Inertia & Energy
Ch 12: Torque & Rotational Dynamics
Ch 13: Rotational Equilibrium
Ch 14: Angular Momentum
Ch 15: Periodic Motion (NEW)
Ch 15: Periodic Motion (Oscillations)
Ch 16: Waves & Sound
Ch 17: Fluid Mechanics
Ch 18: Heat and Temperature
Ch 19: Kinetic Theory of Ideal Gasses
Ch 20: The First Law of Thermodynamics
Ch 21: The Second Law of Thermodynamics
Ch 22: Electric Force & Field; Gauss' Law
Ch 23: Electric Potential
Ch 24: Capacitors & Dielectrics
Ch 25: Resistors & DC Circuits
Ch 26: Magnetic Fields and Forces
Ch 27: Sources of Magnetic Field
Ch 28: Induction and Inductance
Ch 29: Alternating Current
Ch 30: Electromagnetic Waves
Ch 31: Geometric Optics
Ch 32: Wave Optics
Ch 34: Special Relativity
Ch 35: Particle-Wave Duality
Ch 36: Atomic Structure
Ch 37: Nuclear Physics
Ch 38: Quantum Mechanics

Intro to Calculating Work

See all sections
Sections
Intro to Energy
Intro to Calculating Work
Work By Gravity & Inclined Planes
Work By Variable Forces (Springs)
Net Work & Kinetic Energy
More Work-Energy Problems
Power

Concept #1: Work Done by a Constant Force

Practice: You pull a 5-kg object vertically up with a constant 100-N for 2 m. How much work do you do?

Example #1: Work by a Constant Force

Practice: A water skier is pulled by a boat (shown). Both move north with a constant 10 m/s. The tension on the rope is 150 N, and makes an angle of 53° with the horizontal. How much work is done by the rope in 5 seconds?

Concept #2: Zero Work, Negative Work & Work by Friction

Practice: A 3-kg box sits on a level surface. The box-surface coefficient of friction is 0.4. You pull on the box with 20 N at 37o above the horizontal for 5 meters. Calculate the work done by: 

(a) you;
(b) friction;
(c) weight; and
(d) normal.

How much energy was dissipated? Where did this energy “go” ?

Additional Problems
A 5 kg mass is pushed across a floor with a coefficient of kinetic friction of 0.35. If the force pushing the mass is 70 N, answer the following question: How much work is done by the pushing force after 5 s? How much work is done by friction after 5 s? How much work is done by the normal force after 5 s? How much work is done by gravity after 5 s?
A constant force of F = (3 N) î - (5 N) ĵ. How much work does this force do on a 1.4 kg mass if it undergoes a displacement of Δ x = (2 m) î + (4.5 m) ĵ? Assume that the mass moves in a straight line.
A mass of 1kg begins at a position (–3 m, –4 m) at a speed of 4.6 m/s. If it moves in a straight line and ends up at a position (2.5 m, 3 m) at a speed of 3.2 m/s, how much work was done on the mass? What is the net force acting on the mass?
A 5 kg object is under the influence of a conservative force, F = (3N )i - (4.5N)k, and undergoes a displacement of Δx = -(2 m)i + (1 m)j + (6.5m)k. What is the work done on the object? What is the change in the object’s potential energy due to this conservative force?
How much work is done by the following force over the 12 m displacement?
Two men, Joel and Jerry, push against a concrete wall that is 3 meters thick. Jerry stops after 10 min, while Joel is able to push for 5.0 min longer. How does the work that Joel does on the wall compare to the work that Jerry does on the wall?A) Both men do positive work, but Jerry does 50% more work than Joel.B) Both men do positive work, but Joel does 25% more work than Jerry.C) Both men do positive work, but Joel does 50% more work than Jerry.D) Both men do positive work, but Joel does 75% more work than Jerry.E) Neither of them does any work.