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.
Homework Statement
From point A, the marble rests at the height of 0.895 m. Then, it is released up to point B which has a height of 0.665 m. From point B to point C, the marble falls in a projectile motion.
Calculate the Kinetic Energy on position B and the work done by friction from...
Homework Statement
the man having the weight of 75kg is able to run up a 4.5 m high flight of stairs in 4s. determine the power generated. how long would a 100w light bulb have to burn to expend the same amount of energy?
Homework Equations
The Attempt at a Solution
I havnt done...
These are some of my question related to work and energy-
1)W is proportional to Force
W is proportional to displacement
Therefore, W=Fs
My question is why do we have to multiply F and s.Why can't we add them.Why can't the formula be W=F+s
2)In space if you were to push an object it...
I was just confused now. Is there work being done if I lift a bucket of water straight up?
I know there is something about "work being done BY the bucket" and "work being done ON the bucket".
Since I'm not moving horizontally does it mean that no work is done on the bucket?
But I'm still...
Homework Statement
A car of weight 7000N travels at a steady speed of 8m/s up a steady incline at 15degrees above the horizontal. The car's motion is opposed by a constant frictional force of 500N.
Homework Equations
Calculate:
a) the gain in p.e per second
b) the work done per second...
I've always seen Work as an extra mechanic energy given to the system... but i really can't figure it out :
If we lift a 2kg ball, that's steady, using g as 10m/s², with 25N, we'll have a 5N up resultant force...
after its 5meters up, the resultant work will be 25J (5N.5m), but the...
Homework Statement
A block with mass m = 4.00 kg is attached to a spring with spring constant k = 500 N/m, and it slides on a horizontal table that is not frictionless. At a time when the spring is compressed by 3.00 cm, the block is observed to be moving toward the right (decompressing the...
solved! Work and Energy, friction problem
A 1200-kg car is being driven up a 5.0° hill. The frictional force is directed opposite to the motion of the car and has a magnitude of f = 524 N. A force is applied to the car by the road and propels the car forward. In addition to these two forces...
A student, starting from rest, slides down a water slide. On the way down, a kinetic frictional force (a nonconservative force) acts on her. The student has a mass of 70 kg, and the height of the water slide is 11.3 m. If the kinetic frictional force does -7.6 × 103 J of work, how fast is the...
Hello, i appreciate your help!
1. Homework Statement
In this website the drawing of the situation in the first exercise can be seen, for better understanding.
http://wwwprof.uniandes.edu.co/~gtel...s-semana10.pdf
The problem asks me to determine the minimum height h to allow an...
Homework Statement
A cart loaded with bricks has a total mass of 13.8 kg and is pulled at constant speed by a rope. The rope is inclined at 20.8° above the horizontal and the cart moves 30.4 m on a horizontal floor. The coefficient of kinetic friction between ground and cart is 0.7 . The...
Homework Statement
I feel as though I am missing information but I have been assured I'm not can anyone help me out?
At an accident scene on a level road, investigators measure a car's skid mark to be d=88m long. The accident occurred on a rainy day, and the coefficient of friction was...
Homework Statement
A sled is being pulled across a horizontal patch of snow. Friction is neglibile. The pulling force points in the same direction as the sled's displacement, which is along the +x axis. As a result, the kinetic energy of the sled increases by 38 percent. By what percent...
I have attempted to solve this problem repeatedly, but I cannot get a correct answer. Any help would be wonderful.
The Problem
A certain kind of projectile launcher has a spring constant of 50 N/m and you compress the spring 18 cm before it locks. When compressed, the spring is 2 cm tall...
I have attempted to solve this problem repeatedly, but I cannot get a correct answer. Any help would be wonderful.
The Problem
A certain kind of projectile launcher has a spring constant of 50 N/m and you compress the spring 18 cm before it locks. When compressed, the spring is 2 cm tall...
Homework Statement
Some gliders are launched from the ground by means of a winch, which rapidly reels in a towing cable attached to the glider. What average power must the winch supply in order to accelerate a 189-kg ultralight glider from rest to 20.5 m/s over a horizontal distance of 52.2...
Homework Statement
Starting from rest, a basketball rolls from the top of a hill to the bottom, reaching a translational speed of 6.12 m/s. Ignore frictional losses.
Homework Equations
(a) What is the height of the hill?
(b) Released from rest at the same height, a can of frozen...
Peter M McGinnis describes work as being 'the means by which energy is transferred form one object or system to another' in Biomechanics of Sport and Exercise.
Many people explain that deformation of a car striking a solid object or a body striking the ground as the object or ground doing...
Homework Statement
The 2Mg (i assumed mega-gram, not sure if that is the correct term) car has a velocity of v= 100km/h when the driver sees an obstacle in front of the car.
If it takes 0.75 s for him to react and lock the brakes, causing the car to skid, determine the distance the car...
the problem is:
A rubber-band slingshot shoots a 25-gstone. What is the initial speed of the stone if the rubberband is drawnback 0.15m with aforce of 27 N?
m= 25g
d=0.15 m
f= 27 N
v(initial) = ?
Homework Equations
Ep = (1/2)Fx
Ek=(1/2) mv^2
The Attempt at a Solution
so far, I...
Homework Statement
The ends of two identical springs are connected. Their un-stretched lengths Lo are negligibly small and
each has spring constant k. After being connected, both springs are stretched an amount L and their free
ends are anchored at y = 0 and x = ±L as shown . The point...
A 5.0kg mass is initally held at rest, attached to a disk shaped 8.0kg pulley of radius 12.0cm by a massless cord. Using Newton's Laws, find the tension in the cord and the acceleration of the mass falling after it is released.
Please help
The axle of a 12.0kg solid sphere of radius 0.500m is attached to a suspended 5.00kg weight by a massless cord that passes over a frictionless, massless pulley. When the system is released, the mass drops and the sphere rolls without slipping. Find the tension in the cord and the acceleration of...
Homework Statement
A hand exerts a constant horizontal force on a block thatis free to slide on a frictionless surface. The block starts fromrest at point A, and by the time it has traveled a distance d topoint B it is traveling with speed Vb. When the block has traveledanother distance d to...
why work is defined? and when it was defined ( approximately) and who has defined it? It is one of the most important things in physics and I am wondering that is it defined only for make the seeing and understanding things in the nature easier?
Actually I am also wondering about when and...
Homework Statement
Ball with mass m is connected by a strong string of length L to a pivot point and held in place in a vertical position. A wind exerting constant force of magnitude F is blowing from left to right. If the ball is released from rest, show that the maximum height H it reaches...
Question 1:
Homework Statement
Pinkfield slides a 1000 kg piano at a constant speed against a frictional force of 5000 N through a distance of 2.0m
Homework Equations
W = Fa x d?
The Attempt at a Solution
a = 5000/1000 = 5m/s^2
I tried to use this formula i found somewhere :
Ei + Wf = Ef...
Homework Statement
[PLAIN]http://rawrspace.com/physics.GIF
Homework Equations
v=v0+at
x=x0+v0t+(1/2)at2
W=\DeltaK=K2-K1
The Attempt at a Solution
For the first part of this problem I attempted it this way which I think is completely wrong.
I rearranged the first two equations...
Homework Statement
A 2.1 x 10^3kg car starts from rest at the top of a 5.0m long driveway that is inclined at 20degrees with the horizontal. If an average friction force of 4.0 x 10^3N impedes the motion, find the speed of the car at the bottom of the driveway.
Homework Equations...
So work is when a force causes a displacement of an object. So what does it mean when 1.89J of work is done by an applied force? Does it mean this amount of force is needed to cause a displacement? Also how and why does an object store energy? I'm really confused by gravitational and elastic...
1. The energy from elastic potential is 1/2 kx^2. K is a spring constant and x is the displacement distance of the spring from its equilibrium position. How far will a spring of spring constant k=25 N/m compress if an obejct of mass 4 kg has an initial velocity of 20 m/s runs into the spring...
Homework Statement
An acrobat on skis starts from rest 50.0 m above the ground on a frictionless track and flies off the track at a 45.0° angle above the horizontal and at a height of 10.0 m. Disregard air resistance.
a. What is the skier’s speed when leaving the
track?
b. What is the...
Homework Statement
In 1985 in San Antonio, Texas, an entire hotel building was moved several blocks on 36 dollies. The mass of the building was about 1.45 x 10^6 kg. If 1.00 x 10^2 J of work was done to overcome the force of resistance that was just 2.00 percent of the building's weight. How...
Homework Statement
A spring of constant 18 N/cm is compressed a distance 7cm by a 0.5 kg mass, then released. It skids over a frictional surface of length 1.6m with coefficient of friction 0.17, then compresses the second spring of constant 5 N/cm. the acceleration of gravity is 9.8m/s^2...
Homework Statement
I don't know when the work of a spring is negative, and when it's positive... When is the work of a spring negative and when is it positive?
Homework Equations
Wsp= -(1/2)(k)(xf2-xi2)
The Attempt at a Solution
I can get Wsp to be positive when the spring is...
Homework Statement
A weightlifter works out at the gym each day. Part of her routine is to lie on her back and lift a 44 kg barbell straight up from chest height to full arm extension, a distance of 0.54 m.
Homework Equations
If the weightlifter does 24 repetitions a day, what total energy...
Homework Statement
An 80.0-kg man jumps from a height of 2.50 m onto a platform mounted on springs. As the springs compress, he pushes the platform down a maximum distance of 0.240 m below its initial position, and then it rebounds. The platform and springs have negligible mass.
What is the...
Homework Statement
A light inelastic string passes round two small smooth pulleys A and B in the same horizontal line at a distance 2a apart, and carries masses m1 at each end and a mass m2(<2m1) at its middle point. The system is released from rest with m2 at the middle point of AB
By...
1. A spring has a force constant of 30000 N/m.
How far must it be stretched for its poten-
tial energy to be 47 J?
Answer in units of m.
2. A bobsled slides down an ice track starting
(at zero initial speed) from the top of a(n)
94.5 m high hill.
The acceleration of gravity is 9.8 m/s2...
Stuck on some Physics, help please! (Work and Energy)?
K this first one I am not sure how to do it.. i did the second part, that's because i had all the variables but in this one i dont...
ok this is about skeleton racers... the track total height is 104m, in the absence of nonconservative...
Homework Statement
1. A crate with scientific equipment slides down a curved frictionless side of lunar crater of the depth h, and then up along the other side which is an inclined plane as in Figure 2. The coefficient of kinetic friction between crate and incline is k, and the inclined side...
Homework Statement
A 7.8g bullet moving at 575m/s penetrates a tree trunk to depth of 5.50cm. (a) Use work and energy considerations to find the average frictional force that stops the bullet. (b) Assuming that the frictional force is constant, determine hot much time elapses between the...
Homework Statement
Imagine a space station has been built on Venus, and a pendulum is taken outside to determine the acceleration of gravity. The pendulum is a ball having mass m is connected by a strong string of length L to a pivot point and held in place in a vertical position. A wind...
Homework Statement
A crate with scientific equipment slides down a curved frictionless side of lunar crater of the depth h, and then up along the other side which is an inclined plane. The coefficient of kinetic friction between crate and incline is k, and the inclined side makes an angle θ...
Homework Statement
A proton with mass 1.67 x 10^-27 kg is propelled at an initial speed of 3.00x10^5 m/s directly toward a uranium nucleus 5.00 away. The proton is repelled by the uranium nucleus with a force of magnitude F=α/x^2, where x is the separation between the two objects and α =...
Homework Statement
A crate with scientific equipment slides down a curved frictionless side of lunar crater of the depth h, and then up along the other side which is an inclined plane. The coefficient of kinetic friction between crate and incline is k, and the inclined side makes an angle θ...
Homework Statement
A box of mass m can be lifted using a rope and two pulleys, as shown.
http://bcs.whfreeman.com/WebPub/Physics/tiplerphysics6e_bridge/question_bank_images/6-36.png?1341
You exert a force of magnitude F on the free end of the rope. Give your answers in terms of h and w.1...
Homework Statement
How many meters above the ground would a person ( 188.3 lb ) have to climb to gain 3 kilojoules ( 3000 joules ) of potential energy. We usually measure our weight ( W = mg ) in pounds. For conversions, you may need to know that 1 pound is equal to 4.448 Newtons...