Work and Power
A machine performs 438 J of work in 8.3 s. What is the power output of the machine?
52.77 W
To lift a 841 N weight, you apply 159 N of force using a lever. What is the mechanical advantage?
576.54 N
A book with a mass of 1.59 kg is placed on a shelf that is 2.41 m above the ground. What is the potential energy of the book?
37.55 J
What type of simple machine is a slide (pulley, lever, wheel and axle, inclined plane, screw, wedge)? Why?
Inclined Plane: flat sloping surface to slide down
Kinetic energy is the energy of ____________.
motion
A horse pulls a cart with a force of 384 N over a distance of 17.2 meters. How much work is done?
6604.8 J
A lever requires 721 J of work to be applied in order to produce 553 J of work. What is the efficiency?
76.70%
A bowling ball with a mass of 5.3 kg is rolled down the alley at a speed of 8.2 m/s. How much kinetic energy does the bowling ball have?
178.19 J
What type of simple machine is a lightbulb (pulley, lever, wheel and axle, inclined plane, screw, wedge)? Why?
Ideal machines are 100% efficient. They are not possible in real life, as we will always lose some thermal energy to _______.
Friction
If 516 Joules of work are done to move a 11.9 kg object, how far was the object moved?
4.42 m
You apply a force of 137.6 N to an ax in order to split wood. If the ax has a mechanical advantage of 4.19, how much force does the ax do on the wood?
576.54 N
A rock with a mass of 12.75 kg has a potential energy of 491.8 J. How high above the ground is the rock located?
3.94 m
What type of simple machine is an elevator (pulley, lever, wheel and axle, inclined plane, screw, wedge)? Why?
Pulley: it is lifted and lowered using a cord in a grooved wheel
There are 3 classes of lever. For each class tell me what is in the center: the input force, the output force, or the fulcrum (pivot point)
Hint: a binder clip is a 1st class lever
the lever on the hole-punch is a 2nd class lever
the flint striker is a 3rd class lever
1st Class: fulcrum
2nd Class: output
3rd Class: input
A motor has a power output of 1427 Watts. How much work can it do in 26.5 seconds?
37815.5 J
An inclined plane has an efficiency of 64.1%. If 438 J of work is put into pushing a crate up the plane, how much work does the inclined plane do?
280.76 J
A baseball has a mass of 0.154 kg. If it has a kinetic energy of 75.2 J, how fast is the baseball moving?
31.25 m/s
What type of simple machine is a fishing pole (pulley, lever, wheel and axle, inclined plane, screw, wedge)? Why?
Lever: pole that pivots around a fixed point (the handle) (has input force: where you pull, output force: lifting fish, and fulcrum: handle)
Motion must be in the same direction as _______, in order for work to be done.
force
A small motor has a power rating of 57.5 W. If the motor performs 233 Joules of work, how many seconds did it take?
4.05 s
A wheel and axle with an efficiency of 73.2% produces 633 J of Work. How much work must be put into the machine?
864.75 J
A pendulum bob with a mass of 0.63 kg is released from some initial height such that the speed of the bob at the bottom of the swing is 3.1 m/s. What is the initial height of the bob.
0.49 m
What type of simple machine is a doorknob (pulley, lever, wheel and axle, inclined plane, screw, wedge)? Why?
Wheel and Axle: The handle is the wheel which is connected to an axle that spins with the wheel to open the door.
A machine makes work easier by changing the ____ or ____ of a force
size, direction