Chapter 7 & 8 Study Guide

Chapter 8 Study Guide Name ______

Energy Terminology A collision in which objects couple upon impact. Energy is generally lost Inelastic collision to outside the system Work Work: A force applied over a given distance. We do work when we lift a Definition, formula and load against the force of gravity. Both force and movement must occur: units Fd = W (units: Joules) Power Power adds the amount of time required to do the work. Definition, formula and P = Fd/s Measured in J/s or Watts units Kinetic Energy Kinetic energy has both force and distance. Definition, formula and KE = Fd = ½mv2 SI Unit: Joules units As speed doubles, kinetic energy quadruples. Potential Energy Potential Energy: Energy that is stored by virtue of its position. PE = Definition, formula and Fd = mgh SI Unit: Joules units A device used to multiply force or change the direction of force in order to Machine do work

Concept Problems: 1. Regarding an inclined plane, does it take more or less force to push an object up an inclined plane as opposed to lifting it straight up? Does it take more or less work to push an object up an inclined plane? Explain your answer for both. The force is less pushing it up the ramp because the distance is greater. The total work done on the object though is the same (both receive the same resulting potential energy)

Plug and Chug Problems: 2. How much work is done if you lift a 30 kg package 4 m up onto a truck bed? Work = Fd = (30 kg)(10 m/s2)(4 m) = 1,200 J

3. What is the power of a forklift that can lift a 5,000 kg load in 10 meters in 4 seconds? Power = Fd/s = (5,000kg)(10 m/s2)(10 m)/4 s = 125,000 Watts

4. What is the kinetic energy of a 3,000 kg car traveling at a speed of 40 m/s?

KE = ½mv2 = ½(3,000 kg)(40 m/s)2 = 2,400 J

5. What is the potential energy of the same car the very instant it rolls off a cliff 75 m high? PE = mgh = (3,000 kg)(10 m/s2)(75 m) = 2,250 J

6. A machine can lift a 2000 kg package with a 400 N force. What is the mechanical advantage of this machine? F = ma = (2,000 kg)(10 m/s2) = 20,000 N MA = Foutput/Finput = 20,000 N / 400 N = 50