Work
The work done on a system is equal to its change in this.
Energy
An object is dropped from some height. During the drop, the kinetic energy of the object:
Increases
An object is dropped from some height. During the drop, the potential energy of the object
decreases
The unit of power is
Watt (W)
The efficiency of an energy transformation will always be less than this
100%
A student uses a force of 5 N [left] to push a 10-N book 4 m across the floor. The work done by the student on the book is
20 J
A heavy rock and a light rock are dropped from the same height and experience no significant air resistance as they fall. Which one has more kinetic energy at the bottom?
heavy rock
A measure of the AVERAGE kinetic energy of the molecules of a substance
temperature
As the time interval required to do a task increases, the power
decreases
Machine C uses 1000 J of fuel energy to do 200 J of work. The efficiency of machine C is:
20%
The unit of work is the joule (J) which is equivalent to:
kgm2/s2
If the mass of an object is tripled, what happens to its kinetic energy?
tripled (x3)
The energy transformation of a student climbing a flight of stairs.
chemical-kinetic-gravitational
Machine A does 100 J of work in 10 s. Machine B does 100 J of work in 5 s. Which machine has the greatest power output?
Machine B
The useful energy lost by a system during a transformation is usually converted to:
Thermal Energy (friction)
How much work is done if you use 300 N to push against a wall that doesn't move.
0
What speed would a 1200 kg car be moving to have a kinetic energy of 200,000 J
18.3 m/s
Mechanical energy is the sum of
Kinetic and Gravitational
During a physics lab, Jack and Jill ran up a hill. Jack is twice as massive as Jill; yet Jill ascends the same distance in half the time. Who used the most power?
same power
In an energy transformation, the energy output is 30J and the waste thermal energy is 70J. The %eff is?
30%
When is work negative
Force and distance in opposite directions.
If the speed of a car doubles, its kinetic energy
quadruples (x4)
A rollercoaster uses this type of energy to make the ride go.
gravitational
A force produces power P by doing work W in a time T. What power will be produced by a force that does six times as much work in half as much time?
x12
Rearrange the efficiency equation to solve for Eout
Eout = Ein * 100/% Eff