Q1 Chapter 2 - Work, Power, Energy
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What is/are the unit/s used to express Work?
Newton x Meters (NM) or Joules (j) & Ergs
A 10-kilogram box is on a level floor. An applied force of 100 N moves it to the right at a distance of 2 m. Other forces are acting on the box. Calculate the following: 1. The work done by each force. 2. The total work done.
• Work = F_d (Force x displacement) = 100 x 2 = 200 j Work = 10kg x 2m = 98.1 x 2 = 196.2 j • Total Work = W1 + W2 = 200 + 183.6 = 396.2 J
These are the components of calculating work done on an object.
Force applied and Displacement
What is the Formula for Work?
W = Fd
This is the unit of work when centimeter-gram-second (CGS) units are used.
Ergs
Compare Mass and Weight.
Mass > refers to how much matter an object contains > measured in kg > always remains the same > cant be measured directly Weight > refers to force exerted on a mass by gravity > can change with location > can be measured directly using a scale
What is energy? What are its 2 types?
Energy - the capacity to do work Kinetic Energy - the energy due to motion Potential Energy - the energy due to position
1) Give the formula for Kinetic Energy 2) Give the formula for mass when Kinetic Energy and Velocity is Given
• (1/2)mv^2 • 2k ÷ v^2
A 9-kg bowling ball slides on the lane at a velocity of 3 m/s. What is the ball’s Kinetic Energy?
KE = (1/2)mv^2 = (1/2)(9)(3)^2 = 40.5 J
What is the formula used to find the change in Kinetic Energy?
Change in KE = KEf - KEi
What is the Formula used to find KEf and KEi when mass is changing and velocity is constant?
Given Quantities: m1, m2, v KEf = (1/2)(m2)(v)^2 KEi = (1/2)(m1)(v)^2
What is the Formula used to find KEf and KEi when mass is constant and velocity is changing?
Given Quantities: m, v1, v2 KEf = (1/2)(m)(v2)^2 KEi = (1/2)(m)(v1)^2
What are the 3 types of Potential Energy? (there r 4 actually but we only need the 3)
Gravitational Potential Energy - Energy which is in position to object’s position relative to a certain height. Elastic Potential Energy - Energy that is stored in an elastic materials (stretched/compressed). Chemical Potential Energy - Energy that is inherent in all substances like petrol, wood, and plants.
What is the formula used for Ug or Gravitational Potential Energy?
Ug = mgh m - ass g - ravity h - eight
What is the formula used to calculate EPE? (Elastic Potential Energy)
EPE = (1/2)kx^2 U = Elastic Potential Energy k = Spring constant in Nm x = displacement from equilibrium position note: F = kx
What does the Law of Conservation of Mechanical Energy state?
“Energy can neither be created nor be destroyed; it can only be internally converted from one form to another.”
What is the Formula used for the Law of Conservation of Mechanical Energy?
KEi + PEi = KEf + PEf (1/2)(m)(Vi)^2 + mgh = (1/2)(m)(Vf)^2 + mgh