Unit 5 Test Energy Study Guide Flashcards
Define an open system and a closed system, each has three rules:
Nothing can enter
Nothing can leave the system
No external forces act on the system
Define conservation of energy:
The total sum of the energy that you start with you end with
What are 2 situations in which 0 work is done on a system by a force
The force acts perpendicular to motion
There is no motion
What are the units for energy
joules
By definition how is work done to a system and what does it add to a system?
Work is done when a force is applied over a distance. It adds energy to a system
What are the three types of energy and their equations
GPE=mgh
KE=1/2mv²
EPE=1/2kx²
What are the three equations we can use to solve for power
p=w/t
p=f*v
p=change in energy/time
What are the units for power
watts
Two paths lead to the top of a big hill. One is steep and direct, while the other is twice
as long but less steep. How much more potential energy would you gain taking the
longer path?
A) the same
B) twice as much
C) half as much
D) you gain no PE in either case
the same
An object is thrown straight up. Which of the following is true about the sign of work
done by the gravitational force while the object moves up and then down?
A) Work is negative on the way up, work is negative on the way down
B) Work is negative on the way up, work is positive on the way down
C) Work is positive on the way up, work is negative on the way down
D) Work is zero the way up, work is zero on the way down
Work is negative on the way up, work is positive on the way down
By what factor does the kinetic energy (KE) of a car change when its speed is halved?
A) no change at all
B) KE is halved
C) KE is cut to ¼
D) KE is doubled
KE is cut to ¼
How does the work needed to stretch a spring 3 cm compare to the work needed to
stretch it 1 cm?
A) same amount of work
B) 1/3 the work
C) 3 times the work
D) 9 times the work
9 times the work
A car travels with a constant speed of 20 m/s. The car’s engine produces a 4000 N pushing force in order to keep the speed constant. How much power is developed by the engine?
0.005 W
200 W
8,000 W
80,000 W
8,000 W
By what factor does the kinetic energy of a car change when its speed is quadrupled?
no change at all
factor of 2
factor of 16
factor of 4
factor of 16
A roller coaster of mass 400 kg starts its ride from rest at point A. Point A is located at a height of 90 m above the lowest point on the track. The car rolls down the incline and
follows the track around a loop of radius 30 m. Ignore friction force.
a. How much work is required to bring the car to point A?
b. Calculate the speed of the car at point C.
d.Calculate the speed of the car at point B. top of the loop
a = mgh=GPE
4009.890=352,800J
b= GPE = KE
Solve for velocity
d=GPEi-GPE(top of the loop)=KE, solve for v
