Work
What are the units for potential and kinetic energy?
Joules (J)
Give two examples of simple machines and two examples of compound machines
simple: lever, wheel and axel, wedge, screw, inclined plane, pulley
compound: bicycle, scissors, wheelbarrow, can opener
When does a ball rolling down an incline have maximum kinetic energy (at the top, at the bottom, at the middle of the ramp, etc.)?
At the bottom of the incline
If you push an object twice as far without changing the force you pushed it with, what happens to work (increase, decrease, etc.)?
Work doubles!
If Mrs. Suchman pushes against the wall with a 50N force for 2 seconds, how much power is she using?
None! No work is done on the wall.
A 5 kg object is held 5 m above the ground. What is its gravitational potential energy?
250 J
If a pulley does 50 J of work to lift a crate, is this work input or output?
Output
What does the law of conservation of energy state?
Energy cannot be created or destroyed.
If a business man carries a briefcase with an upward force of 10N a distance 5 m to the right, how much work does he do on the briefcase?
He does 0J of work on the briefcase because the force is perpendicular to his displacement
It takes 2 seconds for a pulley to lift a crate weighing 20 N to a height of 10 meters. How much power is required to lift the crate?
100 w
If you double the height of an object, what happens to its gravitational potential energy?
Gravitational potential doubles as well
A person applies a force of 10 N to a lever and the lever applies a force of 50 N to lift an object. What is the mechanical advantage of the lever?
5 N
What type of energy is produced by friction?
thermal energy
What are two ways that work can be increased? (Hint: Work = Force x Distance)
Increase the amount of force applied, increase the distance traveled
What is the relationship between work and power?
Power is the rate at which work is done.
A ball is released from rest at the top of an incline. What type of energy does it have initially, and what energy does it get converted to?
Potential energy to kinetic energy
A machine does 10 J of work and humans must put in 25 J of work. What is the efficiency of the machine?
40%
Plants use this type of energy to create food.
Radiant/solar energy
Student A pushes a box with a force of 5 N 10 meters. Student B pushes the same box with a force of 4 N 12 meters. Who has done more work?
Student A
A man uses 50 N of force to move a box a distance of 10 meters in 25 seconds. How much power did he use?
20 w
An object has a mass of 10 kg and is moving at 2 m/s. What is the kinetic energy of the object?
20 J
How can machines make work easier?
-lowering the force needed to move an object
-increasing the distance an object moves
-decreasing the amount of work needed
A slingshot is pulled back by a kid and then released to shoot a marble at a can. What type of energy is built up by the the rubber band and what type of energy is converted to the marble as it flies through the air?
Elastic potential energy to kinetic energy (mechanical energy)