Vocab
the product of force and distance and cos(theta)
What is work?
rate of doing work
Provide all equations associated with this variable.
what is power?
What is P = Fv
P = E / t
P = W / t
At the top of the loop de loop in a rollercoster, these energies act on the rollercoaster.
What is Potential and kinetic?
This is the Work energy Theorem.
Work equals the total mechanical energy of the system. W = (change in/triangle) E
This system has external forces acting upon it. List an example of this system using the theme of ice skating.
What is an open system?
Example: The system of the male figure skater skates across the ice lifting the female figure skater. External forces include: normal force, force applied by female
Internal force: gravitational force
Energy stored in a compressed object such as a spring.
Us = 1/2 k x2
What is elastic potential energy?
A unit of power which equals to one joule per second
What watt?
Erin is lifting a 7 kg bowling ball up and a distance of 1.2 meters from the ground. Air resistance is not negligible and does work on the ball. When Erin releases the bowling ball, is mechanical energy conserved?
What is no?
Jane pushes an 8kg object in the positive direction. She increases her speed from 2 m/s to 4m/s. What is the change in kinetic energy? How much work was done?
What is 48 joules?
In an open system, mechanical energy may be converted into this type of energy, resulting in a change in the total mechanical energy of the system.
What is Non-mechanical energy or thermal energy due to friction?
Potential energy is stored energy can only be positive. True or False ? Why?
The meaning of zero work is being done.
What is the force being applied is perpendicular to the direction of motion?
You slide a 0.3 kg block up a ramp with a starting velocity of 4.2 m/s. This is the height from the ground that the block will reach on the frictionless ramp.
What is 0.88 meters from the ground?
Erin is lifting a 7 kg bowling ball up and a distance of 1.2 meters from the ground. Air resistance is not negligible and does work on the ball. When Erin releases the bowling ball, its mechanical energy changes by this amount by the time the ball hits the ground. (Use work-energy theorem)
What is 84 joules? What is the ball loses 84 joules of energy?
A girl is practicing her lassoing and tries to reel in a cow. In an open cowgirl-cow system, these objects are providing an external force on the system. List objects and the type of force.
What is...
Earth (force of gravity)
Lasso (Force of tension; Force of lasso on cowgirl)
The big G equation used for the potential energy between objects of LARGE distances.
What is Ug = -Gmm / r ?
Paul and safia both do 1000J of work in the negative direction. Paul completes his work 0.11 seconds faster than Safia. Who did more work? (Show calculations)
Who is Paul?
Sheadon is pushing a ball from a height of 2 meters towards the ground with an initial speed of 3 m/s. What is the final speed of the ball?
What is 7 m/s?
A 20 kg block is slid across a frictional surface with a coefficient of friction of 0.2 a distance of 10 m. What is the change in kinetic energy of the system?
What is the system will lose 400 Joules of energy?
W = (change in) E
W = (change in) K + (change in) U
W = (change in) K +0
- Ff d = (change in) K
-μ Fn d = (change in) K
-μ m g d = (change in) K
-(0.2) (20kg) (10m/s2) ( 10m) = (change in) K
-400 = K
The total mechanical energy of this system remains the same or conserved.
What is a closed system?
I graph Hooke's law F = kx where k is the spring constant, F is Force, and x is the distance compressed or stretched. The slope of a force - time graph will equal this quantity. The graph will be this shape.
What is the spring constant? What is linear?
Paul is lifting a box over his head while jumping on a trampoline. Draw the FBD for the system of Paul. List all external forces. List all internal energies. Derive a work-energy equation.
See board for FBD.
External forces:
Force applied/weight by box
Force of spring by trampoline
Internal energies:
kinetic energy
See board for work-energy theorem.
A 3 kg ball is launched from a table of height 5m to the ground. The ball reaches the ground with a velocity of 8m/s.
Is mechanical energy conserved for the system of the ball-earth? Show calculation.
What is no?
Initial Mechanical energy is 150 J.
U = (3) (10) (5)
Final Mechanical energy is 96 J.
K = 1/2 (3) (8)2
A 10 kg block is slid across a frictional surface with a coefficient of friction of 0.2 a distance of 10 m. What is the change in kinetic energy of the system?
What is the system will lose 200 Joules of energy?
W = (change in) E
W = (change in) K + (change in) U
W = (change in) K +0
- Ff d = (change in) K
-μ Fn d = (change in) K
-μ m g d = (change in) K
-(0.2) (10kg) (10m/s2) ( 10m) = (change in) K
-200 = K
A rock slides down an icy mountain. This is the reason that system of the rock and earth is closed.
What is Total mechanical energy is conserved?
The rock and the earth is included in the system. There are no external forces acting on the system. An icy mountain is also considered frictionless.