Equations to Remember
Energy Types & Conversions
Key Concepts & Vocab
Wild-Card
100
When can you use the equation
W=Fd?
When force is constant (or you're solving for average force)
100
A ball is thrown straight up from the ground. How do the gravitational potential energy, kinetic energy, and total energy of the system change as the ball rises?
Ug decreases, K increases, and the total energy stays constant.
100
What is an open system?
A system with external forces acting on it (usually friction)
100
What are the two forces which commonly cause energy to be dissipated?
Drag & Friction
200
How would you calculate stopping distance given the coefficient of friction, mass, and initial velocity?
1. Calculate the force of friction using
F_f=muF_N
2. Calculate the change in energy as the initial kinetic energy
3. Use W=Fd to solve for the stopping distance.
200
A spring is used to launch a box of mass M up a frictionless ramp. The spring has a constant k and is compressed a distance d. Derive an expression for the velocity of the ball at the top of the ramp at a height of h.
E_"initial"=E_"final"
U_s=K+U_g
1/2kd^2=Mgh+1/2Mv^2
v=sqrt((kd^2-2Mgh)/M
200
What is a linear spring?
A spring which follows Hooke's Law, with the spring force directly proportional to displacement:
F_s=-kDeltax
200
List the 4 typical things which earn you points on a graphing FR question.
1. Labelled Axes with Units
2. Consistent Scaling using at least 1/2 the graph
3. Points Plotted Accurately
4. Line of Best Fit with equal # of points above and below
300
Write two expressions relating potential energy and force using calculus.
F=-(dU)/dx and U=-intFdx
300
The potential energy of a system is represented in the graph below. If the total energy of the system is 0.4 J, what is the kinetic energy of the system when it is at the point labelled Q.
E=K+Ug
0.4=K+(-0.5)
K=0.9 J
300
List the 5 ways of calculating work.
1. W=Fd
2. Area under an F-d graph
3. W=Fdcostheta
4. W=intFdx
5. W=DeltaE
300
A force F(x)=x2+3x3 is exerted on a mass. How would you calculate the average force on the mass as it moves from x=1 to x=2?
1. Integrate to find the work done from x=1 to x=2.
2. Apply W=Fd to find the average force.