What is Work and energy: Definition and 333 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.
I'm confused as to wither or not magnetic fields do work. From reading the forums, as well as my textbook and online resources there seems to be conflicting answers. We talk about magnetic energy, and how work relates to change in energy but then I hear that magnetic fields do no work. Could...
Homework Statement
A motorcycle (mass of cycle plus rider = 250 kg) is traveling at a steady speed of 20 m/s. The force of air resistance acting on the cycle and rider is 200 N. Find the power necessary to sustain this speed if (a) the road is level and (b) the road is sloped upward ar...
Homework Statement
A fight jet is launched from an aircraft carrier with the aid of its own engines and a steam-powered catapult. The thrust of its engines is 230,000 N. In being launched from rest it moves through a distance of 87 m and has a kinetic energy of 45,000,000 J at lift-off.
What...
Homework Statement
A Hot Wheels car, whose mass is 200g is hauling a mass block of 150g along a flat table surface
with a string as shown in the graph below. Assume the car and the attached mass is moving with
an initial velocity of 1.7 m/s. A student predicts that the car will travel a...
1. Homework Statement
Each of the sliders A and B has a mass of 2 kg and moves with negligible friction in its
respective guide, with y being in the vertical direction (see Figure 3). A 20 N horizontal force
is applied to the midpoint of the connecting link of negligible mass, and the...
Homework Statement
Each of the sliders A and B has a mass of 2 kg and moves with negligible friction in its
respective guide, with y being in the vertical direction (see Figure 3). A 20 N horizontal force
is applied to the midpoint of the connecting link of negligible mass, and the...
Homework Statement
A toy car of mass 555g is moving with speed 1.21m/s and strikes a spring mounted to the wall. The spring slows the toy car to rest with a acceleration that varies from 0 - 3.055m/s2.
Determine the spring constant.
Homework Equations
W = -1/2mv2 + 1/2 kx2
The Attempt at a...
Homework Statement
A physics student shoves a 0.50-kg block from the bottom of a frictionless 30.0° inclined plane. The student performs 4.0 J of work and the block slides a distance s along the incline before it stops. Determine the value of s in cm.
Homework Equations...
002 (part 1 of 4)
You throw a softball (of mass .350 kg) straight
up into the air. It reaches amaximum altitude
of 5.8 m and then returns to you.
What is the gravitational potential energy
of the softball at its highest position? Assume
the ball departed fromand returned to ground
level...
Homework Statement
A box has an intial speed of 10 m/s. It slide across a flat section and then up an incline. Use L=20m, \muk=.1, and \theta= 40 degrees. Note that I have not given you the mass. It will cancel out of all the equations in the end.
a. Determine the speed of the box at the...
Ladle Attached to Spring A 0.23 kg ladle sliding on a horizontal frictionless surface is attached to one end of a horizontal spring (with k = 490 N/m) whose other end is fixed. The mass has a kinetic energy of 10 J as it passes through its equilibrium position (the point at which the spring...
Sally applies a horizontal force of 520 N with a rope to drag wooden crate across a floor with a constant speed. The rope tied to the crate is pulled at an angle of 53.0°.
(a) How much force is exerted by the rope on the crate?
Solved and correct.
(b) What work is done by Sally if the...
Homework Statement
1. If a 0.2 kg ball is dropped from a height of 8 m, what is its kinetic energy when it hits the ground?
2. Jane, looking for Tarzan, is running at top speed (4.6 m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she swing upward...
Homework Statement
1. A single force of 5N acts in the x direction on a 8kg object. (a) If the object starts from rest at x=0 at time t=-, find its velocity v as a function of time. (b) Write an expression for the power input as a function of time. (c) What is the power input of the force at...
Homework Statement
Starting from rest, a 5.85 kg block slides 2.07m down a rough 26.4degree incline. The coefficient of kinetic friction between the block and the incline is 0.427. The acceleration of gravity is 9.8m/s^2. Find the work done by the normal force. Answer in units of Joules...
Homework Statement
Problem: Two objects of different mass start from rest, are pulled by the same magnitude net force, and are moved through the same distance. The work done on object A is 500 J. After the force has pulled each object, object A moves twice as fast as object B. (a) How much...
Homework Statement
A 250kg roller coaster passes a point A(located at the top of a hill of height 18.0m) at 12.0 m/s.
What is the speed of the roller coaster at point B located at the bottom of the hill if 8500J of energy is transformed to heat during the journey?
Homework Equations...
Homework Statement
An electric motor and a rope are used to pull a 10kg crate of car parts up an inclined plane. The crate starts out from rest on the ground and ends up with a speed of "vf" at a height of 4.0m above the ground.
The graph provided shows the force exerted on the crate by the...
HELP!Work and energy problem
Homework Statement
A block of mass 1.5kg rests on top of a horizontal table.
a)It is pushed in a straight line a distance of 1.0m in the x-direction, and then in a straight line a distance of 0.5m in the y-direction. If the block is at rest initially and at the...
[b]1. An ice cube is placed on top of an overturned spherical bowl of radius r. (a half circle with a radius r). If the cube slides down from rest at the top of the bowl, at what angle(o) does it separate from the bowl? (hint: what happens to normal force when it leaves the bowl?)...
Homework Statement
A horizontal force of magnitude F = 150 N is used to push a box of mass m = 18 kg from rest a distance d = 8 m up a frictionless incline with a slope q = 32°.
a, b. and c I already have done
d) How fast is the box moving after this displacement? [Hint: Work-energy...
A machine pushes a 2100kg block from rest to a speed of v, doing 3900 J of work. During this time the car moves 10 meters. Neglecting friction between the floor and the block, what is v?
Work=3900J
d=10 meters
m=2100kg
KE=1/2 x m x v^2
3900=1/2 x 2100 x v ^2
v^2= 3900 x 2 / 2100
v =...
A) the force required to give a helicopter of a mass M an acceleration of .10g upward.
B) Find the work done by this force as the helicopter moves a distance of h upward
I'm not incompetent or totally clueless about this.I know that F=ma and W=Fx
So, my solutions:
a) F=ma
F= .10Mg...
Homework Statement
The two problems below are related to a cart of mass M = 500 kg going around a circular loop-the-loop of radius R = 15 m, as shown in the figures. All surfaces are frictionless. In order for the cart to negotiate the loop safely, the normal force exerted by the track on...
A 8 kg block slides down a frictionless incline making an angle of 70° with the horizontal.
(a) What is the total work done on the block when the block slides 2 m (measured along the incline)?
(b) What is the speed of the block after it has slid 1.5 m if it starts from rest?
m/s
(c) What...
A 2.0kg box slides down a long, frictionless incline of angle 30 degrees. It starts from rest at time t = 0 at the top of the incline at height of 20m above ground.
A) What is the potential Energy of the box relative to the ground at t = 0?
U = MGH where y0 is at the bottom of the incline...
A box slides across a frictionless floor with an initial speed v = 3.5 m/s. It encounters a rough region where the coefficient of friction is µk = 0.6.
a) What is the shortest length of rough floor which will stop the box?
b) If instead the strip is only 0.41 m long, with what speed does the...
Work and energy problems :(
can anyone help me w. these, I am completely lost!
A 0.046-kg ball is dropped froma height of 6m above the ground. When it is 1m above the ground, its velocity will be:
An object is dropped from a small height h above the ground. When its height is 0.5h, its...
A block of mass m is pushed off with an initial speed u so that it moves up a rough plane inclined at an angle @ to the horizontal. the friction between the block and the plane is R. Deduce an expression for the velocity v of the block after it has moved a distance d along the inclined plane...
A girl pushes a 3.0x102N box along the floor for a distance of4.0m. The coeffifient ofkineticfriction is0.33. She then lifts the box straight up 1.2m. What is the total amount of work she has done?
I converted 3.0x102N to kgs and found Ff. Then I found work. Then I found Wgrav.
Now I am...
[SOLVED] Work and energy
Hello, I've been having difficulty with this question...
Homework Statement
A 25.6kg child pulls a 4.81kg toboggan up a hill inclined at 25.7° to the horizontal. The vertical height of the hill is 27.3 m. Friction is negligible. Determine how much work the child...
[SOLVED] Work and Energy Problem
Homework Statement
A force is applied to a rigid body moving it from rest at point (1.00 m, 4.00 m) to rest at point (5.00 m, 8.00 m). The force has an x-component of (3.00 N/m^2)x^2 and a y-component of (3.95 N/m)y. Determine the work done.
Homework...
Homework Statement
The cyclist travels to a point A, pedaling until he reaches a speed Va = 4m/s. He then coasts up freely the curved surface. Determine how high he reaches up the surface before he comes to a stop. Also, what are the resultant normal force on the surface at this point and his...
[SOLVED] work and energy problem
Homework Statement
The first part asks
A car (m = 890.0 kg) traveling on a level road at 27.0 m/s (60.5 mph) can stop, locking its wheels, in a distance of 60.0 m (196.9 ft). Find the size of the horizontal force which the car applies on the road while...
Hi i need help with this problem. The first part asks
A car (m = 890.0 kg) traveling on a level road at 27.0 m/s (60.5 mph) can stop, locking its wheels, in a distance of 60.0 m (196.9 ft). Find the size of the horizontal force which the car applies on the road while stopping on the road. First...
This is an annoying problem for which I have a close answer to, not sure where I went wrong.
Homework Statement
Cannonball Man (mass = 75kg) is stuff into his circus cannon, compressing a giant spring by 1.5 meters. He is launched vertically upward at 5 m/s reaching a maximum height...
[SOLVED] Work and Energy Problems
I have a few work and energy problems I don't understand at all. Please help.
While traveling to school at 27 m/s your car runs out of gas 15 km from the nearest gas station. If the station is 16 m above your current elevation, how fast will the car be going...
[SOLVED] Finding Velocity for Work and Energy Problem
A 2 kg physics textbook is dropped form rest out a window 10 meters above the ground. What is the textbook's speed when it's kinetic and potential energies are equal?
The answer is v = 9.90 m/s.
You would use the equation U = (1/2)kx^2...
Hey,
I have a question that I can't seem to work out...can anybody please help me?!
Question:
An extreme skier, starting from rest, coasts down a mountain slope that makes an angle of 25 degrees with the horizontal. The coefficient of kinetic friction between her skis and the snow is...
Need help please!
Homework Statement
Sam, whose mass is 75 kg, straps on his skis and starts down a 50-m-high, 20 degrees
frictionless slope. A strong headwind exerts a horizontal force of 200 N on him as he skies.
Find Sam's speed at the bottom using work and energy.
Find Sam's speed...
Homework Statement
You are pulling your sister on a sled to the top of a 17.0 m high, frictionless hill with a 10.0° incline. Your sister and the sled have a total mass of 50.0 kg. You pull the sled, starting from rest, with a constant force of 127 N at an angle of 45.0° to the hill. If you...
omg I am so lost for this question,
look at this video first
http://mp.pearsoncmg.com/probhtml/applets/setup5_5_3.html
It shows an elevator with a small initial upward velocity being raised by a cable. The tension in the cable is constant. The energy bar graphs are marked in intervals of...
Homework Statement
A 300 kg piano slides 4.0 m down a 30° incline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40.
Picture attached
(a) Calculate the force exerted by the man...
1. A 2.00 x10^2-N force is pulling an 75.0-kg refrigerator across a horizontal surface. The force acts at an angle of 23.0° above the surface. The coefficient of kinetic friction is 0.200, and the refrigerator moves a distance of 9.00 m. Find (a) the work done by the pulling force, and(b) the...
Homework Statement
A 68 kg in-line skater starts from rest and accelerates at 0.21 m/s square for 15s.
a) Find her final velocty and total kinetic energy after the 15s of travel.
b) If she exerts a breaking frictional force of 280N, find her stopping distance.
Homework Equations...
An object hits a wall and bounces back with half if its original speed. What is the ratio of the final kinetic energy to the initial kinetic energy?
I am not sure I understand the question, is it 1:2?
A ball drops some distance and gains 30 J of kinetic energy. Do not ignore air resistance...
Can work be done on a system if there is no motion?
I would say no, no motion = no energy...
Is it possible for a system to have negative potential energy?
I would say yes, since the choice of the zero of potential energy is arbitrary.
A 500-kg elevator is pulled upward with a constant...
Homework Statement
A 0.010-kg positively-charged particle is accelerated by a uniform electric field directed to the right. The object accelerates from 5.0 to 15.0 m/s while traveling a distance of 0.10 m.
Use the definition of potential energy to determine the change in electric potential...
A 5.0x10^4kg space probe is traveling at a speed of 11,000m/s through deep space. Retrorockets are fired along the line of motion to reduce the probe's speed. The retrorockets generate a force of 4.0x10^5N over a distance of 2500km. What is the final speed of the probe.
For this problem i...
A 5.0x10^4kg space probe is traveling at a speed of 11,000m/s through deep space. Retrorockets are fired along the line of motion to reduce the probe's speed. The retrorockets generate a force of 4.0x10^5N over a distance of 2500km. What is the final speed of the probe.
For this problem i...