Vocab
What is the definition of energy?
the ability to do work or cause change
What is the definition of kinetic energy?
energy in the form of motion
What is the definition of potential energy?
energy that is stored
What is the gravitational force on Earth?
9.8
What is the transfer of energy that occurs when a force makes an object move?
What is work
What is a Joule (J)?
The SI unit for energy
What is the equation for KE?
KE = 1/2 x m x v2
What is the equation for gravitational potential energy?
PE = m x g x h
What are the two kinds of mechanical energy?
Kinetic and Potential
What is the law of conservation of energy?
What is elastic potential energy?
energy stored by something that can stretch or compress
A runner has a mass of 75 kg and is running at 20 m/s. What is their KE?
KE = 1/2 (75) (202)
KE = 15,000 J
A diver has a mass of 62 kg and is standing on a diving board 50 meters high. What is their PE?
PE = mgh
PE = (62)(9.8)(50)
PE = 30,380 J
If a force of 10 newtons moves an object 5 meters in the direction of the force, how much work is done?
W = fd
W = (10 N)(5m)
W = 50 J
If it takes 200 joules of work to move a box 10 meters, what is the force applied to the box?
Force = W / d
F = (200 J) / (10 m)
F = 20 N
energy that is stored in chemical bonds
You serve a volleyball with a mass of 2.1 kg. The ball leaves your hand at a speed of 30 m/s. What is the KE?
(Show all work on the whiteboard)
KE = 1/2 (2.1)(302)
KE = 945 J
A bell at the top of a tower is 45 m high. The bell has a mass of 22.5 kg. What is the PE of the bell?
PE = mgh
PE = (22.5)(9.8)(45)
PE = 9,922.5 J
KE = 1/2 mv2
m = 2 X KE / v2
m = 2 x 87 / 12.52
m = 1.1 kg
If a cat is stuck on a branch 20 meters high and has a gravitational potential energy of 180 J, calculate the mass of the cat.
PE = mgh
m = PE / g x h
m = 180 / 9.8 x 20
m = 0.9 kg
what is the definition of gravitational potential energy?
anything that can fall has stored GPE
A car is traveling with a velocity of 40 m/s and has a mass of 1120 kg. What is the cars KE?
KE = 1/2 (1120) (402)
KE = 896,000 J
A skier at the top of Wachusett mountain (611 meters) and has a mass of 74 kg. What is their potential energy at the top of the mountain?
PE = mgh
PE = (74)(9.8)(611)
PE = 443,097.2 J
Calculate the velocity of an object if the kinetic energy is 84.5 J and the mass is 50 kg.
v = sqroot 2 x KE / m
v = sqroot 2 x 84.5 / 50
v = 1.8 m/s
A motor does 1200 J of work in 20 seconds. What is the power output of the motor in watts?
Power = W/t
Power = (1200 J) / (20 s)
Power = 60 Watts