ENERGY,WORK, POWER, AND MACHINES

ENERGY,WORK, POWER, AND MACHINES IPC Spring 2014

Energy, Work, Power & Machines 1. Energy is the ability to do work. Potential energy – stored energy or energy due to position • PE=m g h • m is mass (kg) • g is gravity (9.8 m/s2) • h is the height of the object (m) Kinetic energy – energy of motion • KE= mv2 /2 • m is mass (kg) • v is velocity (m/s)

Energy, Work, Power, & Machines • 2. Energy conversion is a changing of one form of energy to another. • 3.The Law of Conservation of Energy states that energy cannot be created nor destroyed, but is only changed from one form to another.

1. After you place a book on a high shelf, we say the book has increased _____. • gravitational potential energy. • elastic potential energy. • chemical energy. • kinetic energy. [Default] [MC Any] [MC All]

2. An empty truck traveling at 10 km/h has kinetic energy. How much kinetic energy does it have when it is loaded so its mass is twice, and its speed is increased to twice? • the same KE • twice the KE • four times the KE • more than four times the KE [Default] [MC Any] [MC All]

3. When you ride a playground swing, your potential energy is greatest at the highest point. • True • False

4. As mass decreases, kinetic energy increases. • True • False

Energy, Work, Power, & Machines • 4. Work is done when a object moves through a distance because of a force acting upon the object. • 5. The following formula is used to calculate work: W=F×d. • W stands for the work done (J) • F stands for the force (N) • d stands for distance (m) • The SI unit for work is the joule (J).

Energy, Work, Power, & Machines • 6. Power - the rate at which work is done. • 7. Power can be calculated by using the following formula: • P = W/tor P = F×d/t • P stands for power (W) • W stands for work (J) • t stands for time. (s) • The SI unit for power is the watt (W).

5. A student weighing 900 N runs to the top of an 8 m staircase in 5 sec. How much power was produced? • 56.25 W • 11.25 W • 1440 J • 1440 W [Default] [MC Any] [MC All]

6. The metric unit for work is the _________________. • Watt • Joule • Newton • Foot-Pound [Default] [MC Any] [MC All]

7. The metric unit for power is a _____________. • a. Joule • Watt • Newton • Horsepower [Default] [MC Any] [MC All]

8. How muchwork does Billy perform if he pushes the 8000 N stalled car a distance of 25 meters? • 320 J • 100,000 J • 200,000 J • 8025 J [Default] [MC Any] [MC All]

Simple Machines

Inclined Plane A plane is a flat surface. When that plane is inclined, or slanted, it can help you move objects across distances and that's work! A common inclined plane is a ramp. Lifting a heavy box onto a loading dock is much easier if you slide the box up a ramp--a simple machine.

Wedge • You can use the edge of an inclined plane to push things apart. Then, the inclined plane is a wedge. So, a wedge is actually a kind of inclined plane. An axe blade is a wedge. Think of the edge of the blade. It's the edge of a smooth slanted surface.

Screw A screw an inclined plane wrapped around a cylinder A screw can convert a rotational force (torque) to a linear force and vice versa.

Lever • Any tool that pries something loose is a lever. A lever is a rigid bar that "pivots" (or turns) against a "fulcrum" (or a fixed point).

Wheel and Axle • It is two circular objects attached together about a common axis • Wheel is the large cylinder • Axle is the small cylinder

Pulley • In a pulley, a cord wraps around a wheel. As the wheel rotates, the cord moves in either direction. Now, attach a hook to the cord, and you can use the wheel's rotation to raise and lower objects.

Energy, Work, Power, & Machines • 8.The mechanical advantage is the number of times a machine multiplies an effort force. Mechanical advantage can be calculated by the following equations: • AMA = Fr IMA = de Fedr • AMA = actual mechanical advantage (real life) • IMA = ideal mechanical advantage (pretend) • Fr = resistance force de = effort distance • Fe = effort force d r = resistance distance • 9. The mechanical advantage of a pulley system is determined by counting the number of strands of rope that support the resistance force.

Energy, Work, Power, & Machines • 10.Work input is always greater than work output due to friction. Win= W out Fe x de = Fr x d r • Win = work input (J) • W out=work output (J) • Fe= effort force (N) • de= effort distance (m) • Fr =force of the resistance (N) • d r=how far the resistance moved (m)

Energy, Work, Power, & Machines • 11.Efficiencyis a measure of how much of the work put into a machine is changed to work put out by the machine. • Efficiency is calculated using the following formula: • efficiency = W out x 100% Win • efficiency = AMA x 100% IMA

Efficiency of a Machine 12.The amount of work obtained from a machine is always less than the amount of work put into it. This is because work is lost to friction. Efficiency = output work / input work x 100 Remember that work = force x distance

Energy, Work, Power, & Machines • 13. Compound machines consist of two or more simple machines.

9. When 100 J are put into a device that puts out 40 J, the efficiency of the device is • 40%. • 50%. • 60%. • 140%. [Default] [MC Any] [MC All]

10. Which pulley has the greatest mechanical advantage? • A. Picture 1 • B. Picture 2 • C. Picture 3 • D. Picture 4 [Default] [MC Any] [MC All]

ENERGY,WORK, POWER, AND MACHINES