Download Physics 30 – Mechanical Energy Unit REVIEW

Physics 30 – Mechanical Energy Unit REVIEW
Energy, Work, and Power
- Work is the amount of force required to change the position of an object
- Work and Energy are scalar quantities; they are measured in ______________.
- The only force that does work on an object is parallel to the displacement of the object.
- Negative work is done when the only forces applied to the mass are opposite to the direction of motion.
- No work is done when the force acting on the object is perpendicular with the direction of motion.
- Work done on an object is equal to the change in kinetic energy and the change in potential energies 
W = _________________
Power is the rate at which work is done. P = _________________
- Power refers to the strength and speed of an object. P = _________________
- Power is measured in ________________
- Kinetic energy is the energy of a mass while it is in motion. Ek = ______________
- Kinetic energy is dependent on ____________ and ________________
- Kinetic energy is always a positive value, but the change in kinetic energy may be negative.
- Momentum is a vector quantity. p = mv
- A mass only has momentum if it is moving, and that momentum can be changed.
- When a force acts on an object with momentum, it will change its momentum due to Newton’s first law.
- The impulse is the measure of the force acting on the mass for a given time which causes the change in
momentum.  J = F∆t = ∆p
- An impulse is also a vector quantity. J = ∆p = m×∆v
- Objects in a collision undergo an impulse, and due to Newton’s third law, they are equal and opposite of each
other.
- Energy is transferred in collisions, sometimes elastically, sometimes inelastically. Know the difference.
- Gravitational Potential energy is the amount of energy stored in the object when it is elevated to a higher
position. 
U = ___________________
- Gravitational Potential energy is dependent on _________, __________ and ________________ of an object.
- Objects in motion may have gravitational potential energy if they change their height.
- Elastic potential energy is the energy stored by stretching or compressing a spring to a new position x. Hooke’s
Law relates the force compressing or stretching the spring to the new position by the spring constant k.
o The equations for force and elastic potential energy are:
 F = _____________
and
Ep = ___________________
You will be expected to perform some basic calculations on potential energy.
-
Mechanical energy is the energy associated with the motion and position of an object. It is the total energy an
object has whether it is in motion or not.
Mechanical energy = Em = _______________________
In an isolated system, the total mechanical energy is conserved _____________________
In a non-isolated system, the total mechanical energy is not conserved _____________________. The energy
lost must be added to the equation in order to balance out. _________________________________________
1. A 10.0 kg block is released from point A. The track is frictionless except for the portion BC, of length 6.00m. The
block travels down the track, hits a spring of force constant k = 2250N/m, and compresses it 0.300m from its
equilibrium position before coming to rest momentarily. Determine:
a. the speed at point B
b. the energy at point C
c. the coefficient of kinetic friction between surface BC and block.
2. Spiderman uses his spider webs to save a runaway train, moving at 20.0 m/s. His web stretches 800 m before
the 10 000 kg train comes to a stop.
a. Assuming the web acts like a spring, calculate the spring constant.
b. Calculate Spiderman’s power to bring that train to a stop.
3. Use the image below for the following questions.
a. How much work is done by the applied horizontal force FP = 150 N on the 18.0 kg block when the force
pushes the block 5.00 m along the 32° frictionless incline?
b. How much work is done by the gravitational force on the block during this displacement?
c. How much work is done by the normal force?
d. What is the speed of the block (assume that it was zero initially at the bottom) after this displacement?
4. A 1 000 kg vehicle travelling westward at 15.0 m/s is subjected to a 10.0 kN·s impulse northward. What is
the magnitude of the final momentum of the vehicle?
5. Two steel pucks are moving as shown in the diagram. They collide inelastically.
a. Determine the speed and direction (angle θ) of the 1.3 kg puck before the collision.
b. How much heat was released in this collision? (ie how much energy was lost?)