What are the units of work?
all of the above
How efficient is a machine that uses 130 J to lift a 50.0 n load 2.0 m?
77%
The law of conservation of energy states that energy...
cannot be created or destroyed
As a dropped penny falls toward the ground, (blank) energy is converted to (blank) energy.
potential, kinetic
A boy pushes on a parked car with a force of 200 N. The car does not move. How much work does the boy do on the car?
zero
A system that receives energy and matter from external sources is called...
open
At the top of it's arc, a thrown ball has (blank) potential energy...
maximum
(Blank) is the ratio of useful work output to work input
Efficiency
What is the work output by a 92% efficient wheel and axle when 75 J of work is input?
69 J
An 84% efficient single pulley is used to lift a 230 kg piano 3.5 m. How much work must be input?
9.4 X 10^3 J
An object has a kinetic energy of 810 J after falling a certain distance. If the mass of the object is 20 kg, what is the speed of the object at this time?
9 m/s
A medicine ball has a mass of 5 kg and is thrown with a speed of 2 m/s. What is its kinetic energy?
10 J
Which of the following is an example of a wheel and axle?
a screwdriver
Which of the following is an example of a third-class lever?
a hand-held boat paddle
What is the mechanical advantage of a single movable pulley?
2
What is the mechanical advantage of a ramp that is 10 meters long and 2 meters high?
5
Calculate the mechanical advantage of a wrench that allows you to move a bolt 0.01 m by moving the handle 0.50 m.
50
(Blank) is defined as the rate at which work is done?
power
How much power is required to do 180 J of work is 2.4 s.
75 w
A pair of tweezers is...
a compound machine made of two third-class levers
A wheelbarrow is an example of a...
second-class lever
A boy exerts an average force of 65 N when he lifts a box 1.2 meters. How much work does he do?
78 J
A first-class lever has the...
fulcrum in the middle
What are the units of power?
all of the above
The efficiency of a ramp is 75%. If the amount of work input is 240 J, what is the amount of useful work output?
180 J
A weightlifter presses a 400 N weight 0.5 m over his head in 2 seconds. What is the power of the weightlifter?
100 watts
The primary source of the suns energy is...
nuclear fusion
A man pushes a crate along a factory floor by exerting a force of 55 N. If the crate moves a distance of 4.0 m, how much work does the man perform?
220 N
An object weighing 75 N is dropped from the top of a building and falls a distance of 28 m to the ground. How much work does gravity do on the object from the time it is dropped to the time it hits the ground?
2,100 J
What is the gravitational potential energy of a 54 kg box that is 8.0 m above the ground?
4,223.6 J
Which of the following is an example of mechanical energy?
potential energy
Which of the following is a compound machine?
a pair of scissors
A machine is a device that...
can multiply and change the direction of an input force
Levers are divided into (blank) classes based on the location of the fulcrum and of the input and output forces.
three
What are the two families of simple machines?
Inclined plane and lever
A ramp is a (blank) that decreases the force required to move an object while increasing the distance the object travels.
machine
Calculate the gravitational potential energy relative to the ground when an 82 kg person climbs to the top of a 2.0 m stepladder.
1.6 X 10^3 J
A wedge is a modified...
inclined plane
What is the mechanical advantage of a ramp 2.0 m long and 0.50 m tall?
4.0
What is the kinetic energy of a 1.40 kg discus with a speed of 22.5 m/s?
354 J
A dog running at a speed of 12 m/s has 1,080 J of kinetic energy. What is the mass of the dog?
15 kg
A pulley with a mechanical advantage of 5.00 is used to lift a bucket weighing 285 N. How much force must be used to lift the bucket?
57.0 N