Types of Energy
What is gravitational potential energy?
Energy due to the height of an object away form Earth.
PE = mgh
What is work in a physics work?
W = Fd
What is the potential energy of a 10 kg mass at a height of 10 meters?
PE = mgh = 10(9.8)(10) = 980 J
What is power?
Rate of doing work
What is the equation for total energy?
Etotal = PE + KE + Eother
What is kinetic energy?
Energy due to motion.
KE = 1/2 mv^2
What is the unit for work?
Joules
What is the kinetic energy of a 5 kg mass that is moving at 2 m/s?
KE = 1/2 mv^2 = 1/2 (5)(2)^2 10 J
What is the unit for power?
Watts
What does conservation of energy mean?
Total energy of an isolated system remains constant.
What is spring potential energy?
Energy due to stretching or compressing a spring.
PE = 1/2 kx^2
How is work related to energy?
W = change in total energy
What is the spring potential energy of a spring with a spring constant of 50 N/m, when it is stretched a distance of 2 meters?
PE = 1/2 kx^2 = 1/2 (50) (2)^2 = 100 J
What are the equations that can be used to calculate mechanical power?
P = W/t = Fd/t = Fv
If an object is dropped from with 100 Joules of gravitational energy, how much kinetic energy will it have before it hits the floor?
100 Joules
What is thermal energy?
Heat energy.
Q = mc change in t
What does negative work mean?
Energy leaves the system. Friction does negative work.
A 20 Kg object has 500 J of gravitational potential energy. What is its distance from the ground?
h = 2.55 meters
A 50 kg student climbs 40 meters in 20 seconds. How much power did she use?
P = mgh/t = 50(9.8)(40)/20 = 980 Watts
If an object is dropped with gravitational potential energy equal to 100 Joules but only has 90 Joules of kinetic energy right before it lands, what happened?
It lost 10 Joules of energy to heat/air resistance.
What is electric energy?
Work or energy stored in a system due to charged particles.
W = qV
How can you find work from a force-distance graph?
Area
A 10 kg moving object has 100 Joules of kinetic energy. What is it's velocity?
KE = 1/2 mv^2
100 = 1/2 (10) v^2
v = 4.47 m/s
A 200 Newton object climbs 20 meters in 5 seconds. What is its power?
P = Fd/t = 200(20)/5 = 800 Watts
If an object is dropped from a height of 10 meters what is it's velocity right before it hit the ground?
gh = 1/2v^2
9.8(10) = 1/2v^2
v = 14 m/s