Definitions/Theory
Two men, Adam and Bert, push against a wall. Adam stops after 10 min, while Bert is able to push for 5.0 min longer. Compare the work they do to the wall.
Neither of them does any work
A hockey puck slides along frictionless ice. Describe the work done on the puck
no Work Done
What is the gravitational potential energy of a 65.0 kg person relative to a position 10.0 m above ground level when the person is 50.0 m above ground level?
25506 J
Ramps are useful because they decrease the amount of what?
Force Required
Negative work is only done when the angle (θ) between the direction of movement and the force applied is
From 90 degrees to 180 degrees
The kinetic energy of an 89.0 kg Physics teacher is 4.45 x 103 J. What is his speed?
10 m/s
How do you describe power?
The rate of doing work
J/S
Change in energy over time
If the velocity of a car is doubled, then its kinetic energy what?
Quadrupled
A 90.0 N box of papayas is pulled 10.0 m along a level surface by a rope. If the rope makes an angle of 20.0o with the surface, and the tension in the rope is 75.0 N, how much work is done on the box by the rope?
704.8 J
A baseball is thrown down from the top of a 1.30 x 102 m building at a speed of 11.0 m/s. What is its speed as it hits the ground?
52 m/s
Which of the following describes a large power output?
a) Work over a long period of time.
b) Accelerating over a long distance.
c) Quickly changing the height of an object.
d) Moving at a high velocity.
c) quickly changing the height of an object
If an object with mass m falls from the top of a building of height h, what expression can determine the object’s speed just as it hits the ground?
sqrt(2*g*h)
Anna and Alison pull on a 10.0 kg box. Anna pulls with a force of 50.0 N to the left while Alison pulls with a force of 40.0 N to the right. The box moves 45m. Calculate the work done by Anna on the box. Work done by Alison on the box. Net work done on the box.
a) 2250 J
b) -1800 J
c) 450J
A 124 kg boulder sits at the top of a hill which is 15 m height. It rolls down to the bottom and reaches a speed of only 10.5 m/s. How much energy is lost due to friction as the boulder rolled down the hill? If the length of the hill was 32 m, what was the force of friction on the boulder?
A) 11,000 J
B) 360 N
You slam on the brakes of your car in a panic, and skid a certain distance on a straight, level road. If you had been traveling twice as fast, what distance would the car have skidded, under identical conditions?
4 times farther
Two grocery store workers are pulling a 125 kg cart up a ramp into their store. The loading bay is 2.0 m heigh. How much work will the workers do on the cart to get it into the loading bay? The rope the workers pull with can only withstand 475N of tension force. How long of a ramp will they need to get the cart into the loading bay?
a) 2452.80 J
b) 5.2 m (d=mgh/T)
A 625 kg roller coaster cart follows the track depicted in the diagram. The track is frictionless, and the cart starts from rest at point A.
What is the total energy of the cart at point A? What is the kinetic energy of the cart at point C? What is the speed of the cart at point B? What affect would increasing the mass have on the energy at point C? What affect would increasing the mass have on the speed at point B?
a) 73575 J
b) 49050 J
c) 14 m/s
d) more energy
e) same speed
How much time does it take a 2.50 kW electric motor to lift a 7.50x103 N weight through a vertical distance of 15.0 m?
45 seconds
P= [mg(delta)h]/t
A box sits at the top of a frictionless ramp which has a height h. The box slides down the ramp to the flat floor which does have a force of friction. The box slides for a known distance of d. What is the coefficient of friction between the box and the floor in terms of h and d?
u = h/d