Work
What is the general formula for work?
force x distance OR force x displacement
What is the formula for gravitational potential energy?
GPE = mgh
Without friction, ______________ energy is constant for all sorts of motion.
mechanical (sum of PE and KE)
What is power?
rate of doing work
What are the units that 'fit' into our equations for the following quantities?
work energy height mass power k gravity
Joules, Joules, Meters, kilograms, Watts, NO UNIT, m/s2
How much work is done by an upward force applied to something moving sideways?
ZERO - only force parallel to motion counts as work
The work-kinetic energy ________________says work done to an object is usually the change in kinetic energy
theorem
What is the KE of a 1250 kg car travelling 11 m/s?
7.6 x 104 J
decreasing KE and increasing PE on the way up, at the top, ALL PE, then increasing KE and decreasing PE on the way down
117 Newtons (the distance isn't needed, force needed to lift something = weight = mg
How is energy stored as gravitational potential energy released?
the thing falls/rolls downward
A child and sled with a combined mass of 50 kg slide down a frictionless hill. The sled starts from rest. What is the mechanical energy of the system?
3600 J
Water flows over a section of Niagara Falls at a rate of 1.2 x 106 kg/s and falls 50.0 m. How much power is generated by the falling water?
5.9 x 108 W
What is the difference between positive and negative work?
negative - force in opposite direction as motion
A person pushes on a box with a force of 40.0 Newtons at an angle 50.0 degrees from horizontal. What is the magnitude of the force that will push the box sideways?
25.7 Newtons
What does a larger or smaller 'k' in elastic potential energy mean?
smaller - stores less energy per stretch distance
A child and sled with a combined mass of 50.0 kg slide down a frictionless hill. The sled starts from rest. How fast is the sled travelling at the bottom of the hill?
12.0 m/s
A cars engine delivers 50.0 horsepower. If 1 hp = 746 Watts, how much time is needed for the engine to do 6.40 x 106 J of work?
17.2 s
2 J of work is done lifting a 180 g apple. How far is it lifted?
1.1 m
As something falls, what happens to the PE, KE, and ME or the object?
KE - increases
PE - decreases
ME - constant (some loss to friction in real systems)
Explain why a roller coaster only has to have energy added to lift it up the first hill
after that it has enough potential energy to convert to kinetic and back to get through the rest