Work
Work is equal (in an equation) to what? There are TWO answers...
What does this assume?
Work = Fnet * displacement
Work = the change in energy.
Assumes that the force and displacement vectors are in the SAME direction!
True or False Kinetic Energy can be negative
False
The equation for Power, which involves work
Power = work/time
Gravitational Potential energy is calculated by using the formula
GPE = mgh
Work also equals (in terms of energy)
The change in Energy
What does a negative Work sign mean?
The net force and displacement vectors are in OPPOSITE directions (180 degrees apart)
Rudolph has a mass of 300 kg and can fly at 5 m/s Donner has a mass of 200 kg and can fly at 6 m/s. Which reindeer has more kinetic energy?
Rudolph
The distance an object is pushed doubles while the time it takes to do the work is cut in half, what happens to the power
4 times greater
If you double an objects height, this happens to your Potential Energy?
Doubles
How do you find the change in kinetic energy?
Final - Initial Kinetic Energy
The direction of the displacement and the direction of the force are PERPENDICULAR TO EACH OTHER. This means that the amount of work done will be...
Zero
This variable in the equation for Kinetic Energy affects the value of Kinetic Energy more than the others.
If the variable is tripled, what happens to the KE?
Velocity.
Nine times greater KE.
This happens to power when you: double the work (2x) and quadruple (4x) the time.
Power decreases by 1/2
In elastic potential energy, what does the k represent?
The spring constant (or how much force is required to stretch or compress it 1 m)?
Which of the following is a form of mechanical energy: a. Internal
b. Electrical
c. Chemical potential
d. Gravitational potential
D
A 2kg box at rest is 5m high and set falling into motion. The box is going 10m/s at the bottom. How much work did gravity do on the box?
100J (or 98J if g=9.8)
The work from gravity transformed 100J of PE into KE
A pendulum is swinging back and forth (think of an old grandfather clock).What type of energy is held by the pendulum at the lowest point? What type of energy is held by the pendulum at the highest point?
Lowest = KE
Highest = PE
How much power is required to take a 1500kg car from 10m/s to 20m/s in 10s?
22,500 Watts
[1/2(1500)(202)-1/2(1500)(102)]/10
An arrow is shot down from a rooftop at a velocity of v, a second one is shot from the same rooftop upward at a velocity of v, a third is shot purely horizontally at a velocity of v on the same rooftop. Which arrow has more kinetic energy when it reaches the ground? (all are shot from the same height)
None of them (all are equal).
[Gravitational PE of the archer/arrow on the rooftop building + KE from the arrow's initial velocity]
This type of energy increases when there is friction.
Thermal / Heat Energy
A lift machine raises a 506 Newton box from the ground to a height of 19.8 meters in 15.6 seconds. What is power required of the motor to do this task?
642 Watts
A 2 kg ball is dropped off a 10 meter cliff. It has this much Kinetic Energy when it hits the ground
196 J
During peak shopping season at Northbrook Court, an escalator elevates 851 passengers a vertical distance of 8.70 meters over the course of 21.2 minutes. If the average mass of the passengers are 51.3 kg, determine the power required by the motor.
2926 Watts
A jolly 125 kg person holding a sack that weighs 25 kg stands on a rooftop that is 15 meters tall. The potential energy of this person and sack is...
22,500 J
A boy is pulling a wagon along the sidewalk. It has a kinetic energy of 17.7 Joules. The boy then applies a forward force of 26.6 Newtons for 3.52 meters. What is the new kinetic energy of the wagon?
111 Joules