physics: work
How much work is required to lift a 300-kg refrigerator to the second-story level?
1.8×104 J. (multiply then scientific notation)
About 40 J is required to push a crate 4 m across a floor. If the push is in the same direction as the motion of the crate, the force on the crate is about
10 N. (divide)
The power expended doing 100 J of work in 50 s is
2 W. (divide)
Ideally, find the force that is required to lift the piano.
310 N
The work done in pushing a TV set a distance of 2 m with an average force of 20 N is
40 J.
When the useful energy output of a simple machine is 100 J, and the total energy input is 200 J, the efficiency is _______.
50 %.
A toy elevator is raised from the ground floor to the second floor in 20 seconds. The power needed using 1000 J of work, is
50 W. (divide)
A jack system will increase the potential energy of a heavy load by 1000 J with a work input of 2000 J. The efficiency of the jack system is
50%.
Danny Diver weighs 500 N and steps off a diving board 10 m above the water. Danny hits the water with kinetic energy of
5000 J. (multiply)
The power required to exert 4-N force over 3 meters in 2 seconds is
6 W. (multiply then divide)
If an input of 100 J in a pulley system increases the potential energy of a load by 60 J, what is the efficiency of the system?
60%
What is the gain of potential energy of the barbell when it is lifted to this height?
720 J.
Calculate the work done in lifting a 600-N barbell 1.2 m above the floor.
720 J. (multiply)
A 2-kg ball is held 4 m above the ground. Relative to the ground its potential energy is
80 J.
Calculate the kinetic energy of an 84-kg scooter moving at 14 m/s .
8200 J. (idk how to do this)
Calculate the work done when a 24-N force pushes a cart 3.6 m .
86 J. (multiply)
Rank PE from greatest to least at each point.
AECBD
Which requires more work: lifting a 50-kg sack a vertical distance of 2 m or lifting a 25-kg sack a vertical distance of 4 m?
Both take the same 1000 J.
Rank KE from greatest to least at each point.
DBCEA
Rank speed from greatest to least at each point.
DBCEA
If a machine multiplies force by a factor of 4, what other quantity is diminished, and by how much?
Distance is diminished to one-quarter.
Select the correct equations that show that a machine that has an input of 100 J and an output of 55 J is 55 % efficient.
Efficiency η=(Eout/Ein)⋅100%=((55J)/(100J))⋅100%=55%
Can a machine multiply input force? Input distance? Input energy?
Force: Yes; Distance: Yes; Energy: No
When the speed of a moving car is doubled, how much more kinetic energy does it have?
It has four times as much.
Select the correct equations that show that 32 J of work is done when a 4.0-kg block of ice is moved from rest to a speed of 4.0 m/s.
W=mv2/2=((4.0kg)⋅(4.0m/s)2)/2=32J
Which has greater kinetic energy?
a car of half the mass traveling at 60 km/hr
A feather and a coin dropped in a vacuum fall with equal
accelerations.
Which task requires more work?
both require the same
The bob of a simple pendulum has its maximum kinetic energy at the
bottom of its swing.
The work you do when pushing a shopping cart twice as far while applying twice the force is
four times as much.
When you lift twice the load twice as high, in half the time, the increase in potential energy is _______.
four times.
what is the unit of work
joule
An object has gravitational potential energy due to its
location.
A 1-kg ball dropped from 2 m rebounds only 1.5 m after hitting the ground. The amount of energy converted to heat is about
more than 2.0 J.
An object that has kinetic energy must be
moving.
When a drawn bow of potential energy 40 J is fired, the arrow will ideally have a kinetic energy
of 40 J.
Which requires the most amount of work by the brakes of a car?
slowing down from 100 km/h to 70 km/h
A ball rolling down an incline has its maximum kinetic energy at
the bottom.
When one does twice the work in twice the time, the power expended is _______.
the same.
A 1000-kg car and a 2000-kg car are hoisted to the same height. Raising the more massive car requires
twice as much work.
