What is Work energy theorem: Definition and 108 Discussions
In physics, work is the energy transferred to or from an object via the application of force along a displacement. In its simplest form, it is often represented as the product of force and displacement. A force is said to do positive work if (when applied) it has a component in the direction of the displacement of the point of application. A force does negative work if it has a component opposite to the direction of the displacement at the point of application of the force.
For example, when a ball is held above the ground and then dropped, the work done by the gravitational force on the ball as it falls is equal to the weight of the ball (a force) multiplied by the distance to the ground (a displacement). When the force F is constant and the angle between the force and the displacement s is θ, then the work done is given by:
W
=
F
s
cos
θ
{\displaystyle W=Fs\cos {\theta }}
Work is a scalar quantity, so it has only magnitude and no direction. Work transfers energy from one place to another, or one form to another. The SI unit of work is the joule (J), the same unit as for energy.
Hi,
After reading several resources about work and energy, I am confused about the conditions that should be satisfied in order to be able to apply work energy theorem. It seems that textbooks have different arguments about this issue. I can summarize what textbooks say in three different...
Homework Statement
A 392-N wheel comes off a moving truck and rolls without slipping along a highway. At the bottom of a hill, it is rotating at 25.0rad/s. The radius of the wheel is .6m and its moment of inertia about its rotation axis is 0.800MR2. Friction does work on the wheel as it...
Homework Statement
I do not know how to find the height. I am thinking of using mgh=delta k but I am not getting the correct answer. I know the answer is 6.28m because my teacher gave it to me.
Below is the picture and question:
Homework Equations
mgh = delta kThe Attempt at a Solution
ep=ek...
Homework Statement
A helicopter, starting from rest, accelerates straight up from the roof of a hospital. The lifting force does work in raising the helicopter. An 720-kg helicopter rises from rest to a speed of 7.5 m/s in a time of 5.0 s. During this time it climbs to a height of 7.9 m...
Plz tell me
Which is correct form of Work Energy theorem
1. Total Work = Toatl change in Mechanical Energy(Potental + Kinetic)
2. Total Work + Potential Energy = Total Change in Kinetic Energy
3. Total Work = Total Change in Kinetic Energy (Mention in the textbooks)
Actually i am confused...
Homework Statement
Using work energy theorem, solve:
The Attempt at a Solution
The actual answer (3.11s) is exactly half of my answer. Does anyone know what I did wrong?
Homework Statement
As part of your daily workout, you lie on
your back and push with your feet against a platform attached to
two stiff springs arranged side by side so that they are parallel to
each other. When you push the platform, you compress the springs.
You do 80.0 J of work when...
Homework Statement
At a waterpark, sleds with riders are sent along a slippery,
horizontal surface by the release of a large compressed spring. The
spring with force constant and negligible mass
rests on the frictionless horizontal surface. One end is in contact
with a stationary wall. A...
I just wanted to start a thread about the basic concepts of work and energy to clarify some things I have been wondering about.
Firstly, work and kinetic energy are concepts independent of force fields; right? Am I right to think that the relationship of force and kinetic energy with respect to...
I came across a rather confusing topic about Work Energy Theorem and Potential Energy applied in lifting a particle.I will be glad if anyone clears it for me.
Consider a particle at a height =0.Potential Energy is considered as zero at height=0.Now it is lifted to a position where height is h...
Homework Statement
The Attempt at a Solution
Is this correct? Is the change in potential energy Ufinal-Uinitial?
My answer turns out to be a positive number, so intuitively does this mean that some of the kinetic energy went into potential and thus the final potential energy is greater than...
Homework Statement
Homework Equations
Inertia about pin = ml^2/3
Work done by rotation = M*theta = 0.5(Inertia about pin) *ω2
The Attempt at a Solution
I tried two different methods and both came out to be the same answer. However they did not correspond to any of the multiple...
Just a little confused, when work is done on an object it's energy increases right? (i.e. Work done on object = Change P.E + Change K.E + Work done by object)
So how come when gravitational force does work on an object(i.e. it falls) the potential energy decreases instead.
So its like Work...
Homework Statement
Spiderman, whose mass is 80.0 kg, is dangling on the free end of a 12.0 m long rope, the other end of which is fixed to a tree limb above. By repeatedly bending at the waist, he is able to get the rope in motion, eventually getting it to swing enough that he can reach a...
Homework Statement
A crate of mass 10.0 kg is pulled up a rough incline with an initial speed of 1.5 m/s. The pulling force is 100 N parallel to the incline which makes an angle of 20.0° with the horizontal. The coefficient of kinetic friction is .4 and the cart is pulled 5.00 m.
e) What is...
Homework Statement
A baseball is thrown from the roof of 21.7 -tall building with an initial velocity of magnitude 13.2 and directed at an angle of 55.0 above the horizontal.
What is the speed of the ball just before it strikes the ground? Use energy methods and ignore air resistance...
Homework Statement
A moving electron has kinetic energy K1 . After a net amount of work W has been done on it, the electron is moving one-quarter as fast in the opposite direction.
A) Find W in terms of K1
B) Does your answer depend o the final direction of the electrons motion? No...
If a ball, mass 10kg, is displaced 5m by a gravitational acceleration or 10 m/s², what is the work done by the gravity, and what is the change in kinetic energy of the ball?
problem -
a bullet of mass .012kg and horizontal speed 70meters per second strikes a block of mass 0.4 kg and instantly comes to rest with respect to the block. the block is suspended from the ceiling by means of thin wires . calculate the height through which it rises.
attempt -
total...
Homework Statement
A weapon fired a 25.8-kg shell with a muzzle speed of 880 m/s. What averageforce acted on the shell?Homework Equations
work energy theorem?
The Attempt at a Solution
Can someone please explain where the 6.00 comes from?
Starting from rest, the shell acquired a kinetic...
Mass on an inclined plane with friction!
There is a mass at the bottom of an inclined plane. It travels with an initial velocity up the inclined plane at an angle θ. There is a coefficient of friction on the ramp. How far up the ramp will the mass go before stopping? What is the speed of the...
In my book it is talking about conservation forces and work energy theorem.
In the book it said...
"suppose gravitational potential energy alone does work (constant force)
*Then Wnet = Wg ... ending statement Ef = Ei...
My question... Does the work energy theorem only deal with...
I posted a picture of the paragraph that I am confused about...
The following paragraph says the body accelerates even though the forces are constant...
can some one explain why the acceleration is not zero?
Homework Statement
A toboggan is initially moving at a constant velocity along a snowy horizontal
surface where friction is negligible. When a pulling force is applied parallel to
the ground over a certain distance, the kinetic energy increases by 47%. By what
percentage would the kinetic...
Homework Statement
Hey all! I was given a multi-step problem and solved everything but the last step. Okay so, a mass on a frictionless plane by a string at an angle theta for a distance until it reaches an incline that has friction and is parallel to the string. The problem asks to find the...
what are the limitation work energy theorem ?
this theorem is very helpful in solving questions. But I think there are some limitations of this bold theorem. that is
(1) does not define the direction of velocity &
(2) does not define spontaneity of process, like say there is an body on the...
Homework Statement
Mass m whirls on a frictionless table, held to circular motion by a string which passes through a hole in the table. The string is slowly pulled through the hole so that the radius of the circle changes from l1 to l2. Show that the work done in pulling the string equals...
if a cars mass is 1604 kg and it is traveling at a speed of 60 mph ...then it's KE is .5 X 1604 X 60 squared = a KE of 2,88,200 J ...now...my question is...using the work energy theorem - what is the TOTAL WORK done to get to a speed of 60 mph ??
1. Homework Statement
_>
Suppose the 2.0kg model car is initially at rest at x=0 and F is the net force acting on it. Use the work energy theorem to find the speed of the car at (a) x=3.0m, (b) x=4.0m, and (c) x=7.0m...
Hello :)
Homework Statement
<Q>A wheel of moment of inertia "I" and radius "R" is free to rotate about its center as shown in figure http://s1102.photobucket.com/albums/g448/vissh/?action=view¤t=pulley-1.jpg" .A string is wrapped over its rim and a block of mass m is attached to the...
Homework Statement
The left side of the figure shows a light (`massless') spring of length 0.320 m in its relaxed position. It is compressed to 74.0 percent of its relaxed length, and a mass M= 0.230 kg is placed on top and released from rest (shown on the right).
The mass then travels...
Homework Statement
\SigmaW = \DeltaE
so if we have an elevator getting pulled by force equal to it's weight making it move with a constant velocity then the net force is equal to 0 so the sigma W is equal to zero but isn't there non zero change in potential energy ?
Homework Equations...
Homework Statement
A block with mass 1.50 kg is attached as shown to a spring with a force constant of 456.0 N/m. The coefficient of kinetic friction between the block and the surface on which it slides is 0.210. The block is pulled 3.60 cm to the right of its equilibrium position and then...
Homework Statement
A truck is moving on a level street with speed Vo when the brakes lock (the tires don't roll and skid). Find the minimum stopping distance of the truck in terms of Vo, g, and the coefficient of kinetic friction μk.
Homework Equations
W = F*d
W = K2-K1
K = 1/2mv2...
Homework Statement
A branch falls from the top of a 95.0 m tall redwood tree, starting from rest. How fast is it moving when it reaches the ground?Homework Equations
Total work = \Delta KThe Attempt at a Solution
I have no idea how to do this problem.
So i have this general question.
When the situation arises in which there are velocity and/or position depended forces acting on an object, would it be generally easier to use the work energy theorem or Newton's 2nd law & kinematics in predicting the motion? My guts tell me it will be work...
So, yeah, my midterm is on friday, and i can't even figure out how to do questions like these because i just don't understand the way my prof teaches and the textbook has nothing relevant.
So far, I've used work energy theorem to find the work done to stop the block. then i wrote out a net work...
1. A 0.066 kg arrow is fired horizontally. The bowstring exerts an average force of 50 N on the arrow over a distance of 0.95 m. With what speed does the arrow leave the bow?
2. Work Energy Theorem = change in kinetic energy = (1/2*mass*Final Velocity^2)-(1/2*mass*Initial Velocity^2)...
1. A rescue helicopter lifts a 90 kg person straight up by means of a cable. The person has an upward acceleration of 0.70 m/s2 and is lifted from rest through a distance of 10 m. What is the tension in the cable and how much work is done by the tension in the cable? Use the work-energy theorem...
Hi
I just can't seem to grasp this concept!
Anyone have like a small tutorial for this section or notes on it?
Im in grade 12..
For example a question from the exam...
A person skis down a 20m long snow slope which makes an angle of 25degrees with the horizontal.
The total mass...
Homework Statement
A 6.0 kg box moving at 3.0 m/s on a horizontal, frictionless surface runs into a light spring of force constant 75N/cm. Use the work energy theorem to find the maximum compression of the spring.
Homework Equations
Wtotal=K2-K1
k1=1/2mv^2=27 J
The Attempt at a...
Homework Statement
A car is coasting without friction toward a hill of height 'h' and radius of curvature 'r'.
What initial speed will result in the car's wheels just losing contact with the roadway as the car crests the hill?
Homework Equations
Kinetic Energy = (1/2)(m)(v^2)
Potential...
I don't really have any clue on this problem...
Homework Statement
A sled with mass 8.00 kg moves in a straight line on a frictionless horizontal surface. At one point in its path, its speed is 4.00 m/s. after it has traveled 2.5m beyond this point its speed is 6.00 m/s. Use the work...
Homework Statement
A 0.065 kg arrow is fired horizontally. The bowstring exerts an average force of 70 N on the arrow over a distance of 0.90 m. With what speed does the arrow leave the bow?
Homework Equations
W=Fd
W=KE final - KE initial
KE= 1/2mv^2
The Attempt at a Solution...
Homework Statement
a 20N force acts on a 2 KG object for 3 seconds. If the object was initally at rest, How much work was done in this process? I am having problems working this formula with no distance involved W = Fd
Homework Equations
The Attempt at a Solution
http://img530.imageshack.us/img530/5664/looptheloophg9.gif
The two problems below are related to a cart of mass M = 500 kg going around a circular loop-the-loop of radius R = 8 m, as shown in the figures. All surfaces are frictionless. In order for the cart to negotiate the loop safely, the...
Technically, I don't really have a problem specifically that I need help on solving, but there is a crucial concept that I cannot grasp about the WET, and until I can do so, most WET problems are a pain to me.
My professor gave us two types of formulas for the work energy theorem, stating...
A 65kg bicyclist rides his 8.8kg bicycle with a speed of 14m/s. (a) How much work must be done by the brakes to bring the bike and rider to a stop? (b) How far does the bicycle travel if it takes 4.0s to come to rest? (c) What is the magnitude of the braking force?
So for part (a) the...
A particle moving in the x direction is being acted upon by a net force F(x)=Cx^2, for some constant C. The particle moves from x initial =L to x final=3L. What is Delta K, the change in kinetic energy of the particle during that time?
I tried thih by doing the integral of F(x), replacing x...
Homework Statement
You throw a rock of weight 20.4 N vertically into the air from ground level. You observe that when it is a height 14.9 m above the ground, it is traveling at a speed of 26.0 m/s upward.
Use the work-energy theorem to find its speed just as it left the ground;
Use the...