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Work
Work and KE
Work and PE
Vocab
Throwback
100
How much work is done applying a 6N force to a box while pushing it 3m?
W=f*d W=6*3 W=18 J
100
A ball sits at rest on the ground. A person kicks the ball horizontally, doing 300 J of work on it. How much kinetic energy does the ball possess immediately after being kicked? Ignore friction.
Work done on an object = change in energy The ball has 300 J of kinetic energy.
100
How much work is required to lift a 2 kg rock from the ground so that it has 350 J of PE?
Work = Change in Energy W = 350 J
100
Define Work
Force applied to an object over a distance. W = f*d
100
A car drives 2500 m in 150 s. What is its velocity?
16.67 m/s
200
If a person does 210 J of work while applying a 70 N force to a cart, how far has the cart travelled?
W=f*d 210 = 70*d 3 m = d
200
A car is moving with 5000 J of kinetic energy. If its brakes apply a force of 250 N over a distance of 6 m, how much kinetic energy will remain in the car?
W = f * d W = 250 * 6 W = 1500 J 5000 - 1500 = 3500 J
200
How much work is done lifting a 6 kg object 10 m vertically?
W = Change in Energy PE on ground = 0 J PE in air = mgh = (6)(10)(10) = 600 J Change in energy = 600 J Work = 600 J
200
Define Kinetic Energy
Energy of motion. KE = 1/2 m*v^2
200
Convert 75 kilograms into Newtons.
750 N
300
How much work is done lifting a 5 kg brick 2 m into the air?
5 kg = 50 N W = f*d W = 50*2 W = 100 J
300
A 5 kg cart is rolling at 3 m/s. How much work would be required to bring the cart to a stop?
KE = 1/2 m*v^2 KE = (1/2) * 5 * 3^2 KE = 22.5 J Work = change in energy W = 22.5 J
300
A 2 kg rock is falling through the air and has 1200 J of potential energy at point 1, and then 1000 J of potential energy at point 2. How far has the rock fallen from point 1 to point 2.
Change in energy = 1200 - 1000 = 200 J Change in energy = Work = 200 J W = f*d f = 2 kg * g = 2 *10 = 20 N 200 = (20 N)*d d = 10 m
300
Define Gravitational Potential Energy.
The energy stored in an object as the result of its vertical position or height. PE = m*g*h
300
A book is slid across a flat table from position x1 to position x2. If x1 = 1m and x2 = 6m, what is the vertical displacement of the object?
Vertical displacement = 0m. The object was slid across a flat table, so it's vertical position did not change.
400
How much force must a car's brakes apply if it has to do 5000 J of work to bring a car to a stop in 20 m?
W = f*d 5000 = f * 20 f = 250 N
400
How much work would be required to change the speed of a 20 kg wagon from 10 m/s to 4 m/s?
KE1 = (1/2) (20) (10^2) KE1 = 1000 J KE2 = (1/2) (20) (4^2) KE2 = 160 J Change in KE = 1000 - 160 = 840 J Work required = 840 J
400
A 15 kg steel beam is sitting in the bed of a truck 1.5 m off of the ground. The beam is lifted by a crane to the top of a 30 m building at a constant speed. How much work is done lifting the beam from the truck to the top of the building?
Pe in truck = (15)(10)(1.5) = 225 J Pe on roof = (15)(10)(30) = 4500 J Work = Change in PE = 4500 - 225 = 4275 J
400
State the Work - Energy Theorem.
The work done on a system is equal to its change in energy.
400
Define Velocity
change in distance over time how fast and which direction an object is moving