Work
Kinetic Energy
Potential Energy
Conservation of Energy
Power
100
Definition of work.
What adds or removes energy from a system?
100
Definition of kinetic energy.
What is the energy of an object in motion?
100
Definition of potential energy.
What is the energy stored in an object to relative to position?
100
Definition of conservation of energy.
What is the total energy in a system that is constant?
100
Definition of power.
What is rate at which work is done?
200
The work equation.
What is Fdcosθ?
200
The kinetic energy equation.
What is 1/2mv2?
200
Gravitational and spring potential energy.
What is mgh and 1/2kx2?
200
A 80kg box is at rest at the top of a 56m hill. The box slides down the hill. Find the speed of the box at the bottom of the hill.
33.13m/s
Ei=Ef
Ug=KE
mgh=1/2mv2
80(9.8)(56)=1/2(80)v2
v=33.13
200
Power equation.
What is P=W/t?
300
A man lifts his briefcase up with a force of 10N. He walks the to the right 10m. Find the work done by the man.
What is 0J work done?
Fdcosθ = 10(10)cos(90)=0
300
A 5kg ball rolls on the side of the road at 7.5m/s. Find the KE the ball has.
What is 140.63J?
KE=1/2mv2=1/2(5)(7.5)2=140.63
300
A 5kg ball is held at the top of a 68m building ready to be dropped. Find the gravitational potential energy the ball has.
What is 3332J?
Ug=mgh=5(9.8)(68)=3332
300
A spring is compressed at 7m with a spring constant of 43N. The spring pushes a ball horizontally at a constant velocity of 4.3m/s. Find the mass of the ball.
113.95kg
Ei=Ef
Us=KE
1/2kx2=1/2mv2
1/2(43)(7)2=1/2m(4.3)2
m=113.95
300
A person lifts a 6.1kg box up 40cm in 4.2 seconds. Find the rate at which work is done.
What is 5.69 Watts?
P=W/t
Fdcosθ /t=mgdcosθ /t
=6.1(9.8)(.40)cos(0)/4.2=5.69
400
A girl pushes a shopping cart 40m. She exerts a constant force of 13N at an angle of 55O below the horizontal. Find the work done by the girl.
What is 298.26J?
Fdcosθ =13(40)cos(55)=298.26
400
An 3kg object has 30J of KE. Find the speed the object is moving at.
What is 4.47m/s?
KE=1/2mv2
30=1/2(3)v2
v=4.47
400
A spring is compressed 3m. The spring constant is 75N. Find the spring potential energy.
337.5J
Us=1/2kx2=1/2(75)(3)2=337.5
400
A 5kg ball is dropped at a height of 10m. A frictional force acts against the motion with a force of 5N. Find the speed of the ball has right before it hits the ground.
What is 13.3m/s?
Ug+Wf=KE
mgh+Fdcosθ =1/2mv2
5(9.8)(10)+5(10)(cos180)=1/2(5)v2
v=13.3
400
A person uses 89 watts of power to lift a box up to the top shelf. The top shelf is 35m above the ground. It takes them 2.1 seconds to reach it. Find the amount of force the person use to lift the box to the top self.
What is 5.34N?
P=W/t=Fdcosθ/t
89=F(35)(cos0)/2.1
F=5.34
500
Work is done by a force which move it from 0m to 3m. The force is F(x)=3x2+2x. Find the work done by the force.
What is 90J?
W=∫Fdr=∫03 (3x2+2x)dx=[x3+x2]|03= 90-0=90
500
A 68kg person runs rest. They start running for 30m at a constant speed of 5m/s. Find the change in kinetic energy.
What is 850J?
ΔK= KEf-KEi=1/2mv2f-1/2mv2i
1/2(68)(5)2-1/2(68)(0)2=850-0=850J
500
A box is dropped off the top of a 15m building. Right before it hits the ground it has a velocity of 6.6m/s. Air resistance removes 3J of energy from the system. Find the potential energy that was stored in the box before being dropped.
What is 29.4J?
Ug+Wf=KE
mgh+Wf=1/2mv2
m(15)(9.8)-3=1/2m(6.6)2
168.78m=3
m=.02
mgh=(.02)(9.8)(15)=29.4
500
A spring with a constant of 35N is compressed 6cm. When released, the spring pushes a ball up an incline of 36 degrees. The ball moves 5.3m/s past a point on the incline. The point has a height of 36m. Find the gravitational energy the ball has at the point.
What is 6.06J?
Us=KE+Ug
1/2kx2=1/2mv2+mgh
1/2(35)(.06)2=1/2m(5.3)2+m(9.8)(36)
0.063=366.845m
m=1.72x10-5
mgh=1.72x10-5(9.8)(36)
Ug=6.06
500
A person is pulling a 90kg box horizontally. There is a frictional force of 30N acting against the horizontal motion. The person pulls the box at a constant velocity of 5.6m/s. Find the power the person used.
What is 168 Watts?
P=W/t=Fdcosθ/t
ΣF=Fapp-Ff=ma=0
Ffdcosθ/t=30dcos(0)/t=30d/t=30(5.6)/1=168