Work-energy Definition and 168 Threads

On an essentially frictionless, horizontal ice rink, a skater moving at 6.0 m/s encounters a rough patch that reduces her speed by 42 \% due to a friction force that is 20 \% of her weight. Use the work-energy theorem to find the length of this rough patch. i do: [.42 * (.5) * (6)^2]/ [.2...

Homework Statement Suppose a skater is sliding down a parabolic track of known height of 12 meters. You are also given the quadratic equation of the track in terms of x and y, which are in meters. Neglecting friction, how would you find the contact force between his wheels and the track at...

Homework Statement It takes 241 kJ of work to accelerate a car from 22.0 m/s to 28.8 m/s. What is the car's mass? W = 241000 J vo = 22.0 m/s vf = 28.8 m/s m = ? Homework Equations KE = 1/2 mv2 W = KEf - KEo The Attempt at a Solution W = KEf - KEo W = 1/2 mvf2 -...

1. You are a member of an alpine rescue team and must project a box of supplies, with mass m, up an incline of constant slope angle alpha so that it reaches a stranded skier who is a vertical distance h above the bottom of the incline. The incline is slippery, but there is some friction present...

Homework Statement Use the Work-Energy Theorem to show that an object with initial velocity vo will travel a distance d across a rough horizontal surface before stopping, where d = vo2/(2muKg). Homework Equations W = delta KE = mV^2/2 The Attempt at a Solution To be honest, I have...

Homework Statement Problem A skier starts from rest at the top of a frictionless incline of height 20.0 m which makes an angle of 20 degrees with the horizontal. As the bottom of the incline, the skier encounters a horizontal surface where the coefficient of kinetic friction between skis...

Homework Statement If the speed of a car is increased by 50%, by what factor will the minimum braking distance be increased assuming all else is the same? Ignore the driver's reaction time. Homework Equations W = Fd \cdot cos\theta W = \Delta{E_k} The Attempt at a Solution...

[SOLVED] Work-Energy Theorum: Spring potential energy vs Kinetic Energy Homework Statement A 1350-kg car rolling on a horizontal surface has a speed v = 40 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.5 m. What is the spring constant of the...

Homework Statement A spaceship of mass 5.00 x 104 kg is traveling at a speed 1.15 x 104 m/s in outer space. Except for the force generated by its own engine, no other force acts on the ship. As the engine exerts a constant force of 4.00 x 105 N, the ship moves a distance of 2.50 x 106m in...

Homework Statement 2 large metal sheets are separated by a potential of 40 volts by a vaccum. When the proton particle (mass 1.67x10e-27 kg)is released close to the (+) sheet it moves closer to the (-) sheet by way of electric field. What's the KE right before the proton smacks the other...

1. A crate of mass 10kg is accelerated up a rough incline with an initial speed of 1.5m/s. The pulling force is 100N parallel to the incline, which makes an angle of 20deg with the horizontal. The coefficient of kinetic friction is 0.40 and the crate is pulled a distance of 5.0m. Use the...

Homework Statement Rocket launched runs out of fuel after accelerating "for a short distance," coasts to a maximum altitude, then falls back. Known: rocket mass, max. altitude, g. Find velocity when rocket runs out of fuel. Homework Equations There doesn't seem to be enough information...

Homework Statement So I am going over some old problem as review. I have the solution to this problem and something is bothering me about it. Here is the problem and solution:what bothers me is this: When they are finding the expression for the kinetic energy of the disk, they use I about...

Please help! Somple Work-energy problem! Sam works at an amusement park. A boat of children on a water ride comes the the pier at the end of the ride. They are moving at a constant speed of 1.2 m/s, and the loaded boat has a mass of 1200kg. Sam slows the boat down by pushing on it until it...

A 2.20kg textbook is forced against a horizontal spring of negligible mass and force constant 220 N/m, compressing the spring a distance of 0.270 m. When released, the textbook slides on a horizontal tabletop with coefficient of kinetic friction 0.30. Use the work-energy theorem to find how far...

Homework Statement How much work is needed for a 71 kg runner to accelerate from rest to 10.2 m/s? I have no idea how to do this so I have no equations or attmpts at this.

Homework Statement An 1,100 kg car is traveling 46 km/h on a level road. The brakes are applied long enough to remove 51 kJ of energy. A. What is the final speed of the car? B. How much more kinetic energy must be removed by the brakes to stop the car? C. Is this energy really being...

I am just confuse in this question may be i forgot about work and energy .I just need little help not the answer ,here is the question 1.A block of mass 2.2 kg, which has an initial velocity of 3.9 m/s at time t = 0, slides on a horizontal surface. Calculate the work that must be done on...

Homework Statement Select T-True, F-False, for each statement. If the first is T and the rest F, enter TFFFFF. A) The work done to raise a box onto a platform depends on how much time it takes to raise it. (Neglect friction, assume it starts on the ground at rest, and ends up resting...

Homework Statement A 16 g bullet is accelerated in a rifle barrel 72.3 cm long to a speed of 1010 m/s. Use the work-energy theorem to find the average force exerted on the bullet while it is being accelerated. Answer in units of N.Homework Equations W=changeKEThe Attempt at a Solution...

Homework Statement Use the work-energy theorem to solve. A branch falls from the top of a 95 m tall tree, starting from rest. How fast is it moving when it reaches the ground? Neglect air resistance. Homework Equations work-energy theorem:w_total=K_2-K_1 In this problem, K_1 is 0 since it is...

A rope and pulley have negligible mass, and the pulley is frictionless. The coefficient of kinetic friction between the first block (8 kg) and the table is \mu=.250. The blocks are released from rest. USE THE ENERGY METHODS TO CALCULATE THE SPEED OF BLOCK 2 (6 kg) after it has descended 1.5...

1. The hammer throw is a track-and0field event in which a 7.3-kg ball (the hammer), starting from rest, is whirled around in a circle several times and released. It than moves upward on the familiar curvinf path of projectile motion. In one throw, the hammer is given a speed of 29 m/s. For...

OK, I'm working on a question regarding IRFs, but I seem to be a little confused. Question: Observer A is on the ground and Observer B in on a train moving with uniform velocity v wrt the ground. Each observes that a particle of mass m, initially at rest wrt the train, is acted upon by a...

I am having trouble deciding when to use the work-energy formula; change in KE=W and derivations of this formula, or the Kf+Uf+Eth=Ki+Ui+Wext formula when presented with work problems. Are there any type of guidelines or hints that anyone could give me so I can more easily decide which...

Two masses are connecte by a ligh string over a light, frictionless pulley the table surface that m2 is on is also frictionless. Apply the work-energy theorem for this system to calculate the speed of the masses after the masses have moved a distance delta x starting from rest. Note that the...

It's been a while since I've taken calculus. I was going through the derivation of the work-energy theorem and came across this: dv/dt = (dv/dx)(dx/dt) which is supposed to be a result of the chain rule. Anyone care to explain and please simplify it as much as possible. Thanks!

Work-Energy!Help Homework Statement An object of mass 0.550kg is lifted from the floor to a height of 3.50m at a constant speed. A) how much work is done by the lifting force? W=fdotD w=mg*d=.550*9.8/3.5=18.87J is this right B) how much work is done by the Earth on the object? this...

Okay, I just took a test where there was a loop with a bar and a resistor in a magnetic field going into the screen as follows ____/\/\/\_____ lxxxxxxxxxxxxxxxlxxx lxxxxxxxxxxxxxxxlxxx lxxxxxxxxxxxxxxxlxxx lxxxxxxxxxxxxxxxlxxx l____(bar)_____lxxx lxxxxxxxxxxxxxxxlxxx lxxxxxxxxxxxxxxxlxxx...

quick question: I have to write about the work-energy theorem, and I've already defined it, but i need to mention a couple of cases where this theorem is applied in daily life around us.. I dont' quite understand where we would use this theorem in everyday life.. just a few simple ideas to...

A particle moving in the x direction is being acted on 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 deltaK, the change in kinetic energy of the particle during that time? Express your answer in terms of C and L. I got 16CL^3...

Homework Statement You are a member of an alpine rescue team and must get a box of supplies, with mass 2.60 kg, up an incline of constant slope angle 30.0\circ so that it reaches a stranded skier who is a vertical distance 3.10 m above the bottom of the incline. There is some friction present...

[SOLVED] Work-Energy Theorem I'm sorry that I do seem to require quite a bit of help, but sometimes when the formulas just aren't working for me I get desperate. Homework Statement A force is applied to a 2.5kg- radio-controlled model car parallel to the x-axis as it moves along a...

[SOLVED] Please Check to See if I'm Doing Work-Energy Problem Correctly Homework Statement A child riding a bicycle has a total mass of 40 kg. The child approaches the top of a hill that is 10 m high and 100 m long at 5 m/s. If the force of friction between the bicycle and the hill is 20 N...

[SOLVED] Another work-energy theorem problem... Homework Statement An automobile traveling at 45 km/h is brought to a stop in 60 m. Assuming that the same conditions (same braking force, neglect reaction time) hold for all cases, (a) what would be the stopping distance for an initial speed...

[SOLVED] Homework Problem about the Work-Energy Theorem Please help! This is my first year of taking physics and I am really confused... A puck on a shuffleboard decreases in speed from 1.0 m/s to .20 m/s while traveling 4.0 m. What is the coeffecient of kinetic friction between the puck and...

Homework Statement A 5.0 kg box slides down a 5-m-high frictionless hill, starting from rest, across a 2-m-long horizontal surface, then hits a horizontal spring with spring constant 500 N/m. The other end of the spring is frictionless, but the 2.0-m-long horizontal surface is rough. The...

[SOLVED] Work-Energy Principle 1. The problem... On an essentially frictionless horizontal ice-skating rink, a skater moving at 3.00 m/s encounters a rough patch that reduces her speed by 45.0 % to a friction force that is 25.0 % of her weight. Use the work-energy principle to find the length...

[SOLVED] Work-Energy Method Homework Statement A car is stopped by a constant friction force that is independent of the car's speed. By what factor is the stopping distance changed if the car's initial speed is doubled? (Solve using work-energy methods.) Homework Equations Wtotal = delta K...

Is this expression always true?: W=\Delta E Please explain why this is using mathematical computations. I understand it conceptually but I just can't connect the two mathematically. Also, why does my book only have the expression: W= \Delta KE rather than: W= \Delta KE + \Delta PE why did...

A ball is launched as a projectile with initial speed v at an angle theta above the horizontal. Using conservation of energy, find the maximum height h_max of the ball's flight. Express your answer in terms of v, g, and theta. My energy equation is as follows: 0.5m(v^2)cos(theta)...

Homework Statement I have worked out at problem using the conservation of mechanical energy and the answer is correct. I have also worked out the problem using kinematics and got the same answer. My problem is that I can't wrap my brain around why it works out using the conservation of...

Two blocks with different mass are attached to either end of a light rope that passes over a light, frictionless pulley that is suspended from the ceiling. The masses are released from rest, and the more massive one starts to descend. After this block has descended a distance 1.00m , its speed...

A ball is launched with initial speed v from ground level up a frictionless slope. The slope makes an angle theta with the horizontal. Using conservation of energy, find the maximum vertical height hmax to which the ball will climb. Express your answer in terms of v, g, and theta. You may or...

Homework Statement A driver in a car is on a level road traveling at a speed of "v". He puts on the brakes and they lock and skid rather than roll. I have to use the Work-Energy Theorem to give an equation for the stopping distance of the car in terms of "v". the acceleration of gravity "g"...

I am compleatly lost on these two KE Work-Energy Theorem Problem questions any feedback or help would be greatly appreciated. Thank you in advance... 1.) 47.0 g golf ball is driven from the tee with an initial speed of 52.0 m/s and rises to a height of 25.0 m. (a) Neglect air resistance...

Take Two: problem using Work-Energy Theorem The only force acting on a 1.5 kg body as it moves along the positive x-axis has an x component Fx = - 6x N, where x is in meters. The velocity of the body at x = 3.0 m is 8.0 m/s. (a) What is the velocity of the body at x = 4.0 m? (b) At what...

This is the problem: You throw a 20-N rock vertically into the air from ground level. You observe that when it is 15.0 m above the ground, it is traveling at 25.0 m/s upward. Use the work-energy theorem to find a) its speed just as it left the ground; b) its maximum height. I drew a...

Please check to see if my calculations are correct. I am unsure if I used the right values and setup. You throw a rock of weight 21.0 N vertically into the air from ground level. You observe that when it is a height 14.8 m above the ground, it is traveling at a speed of 25.7 m/s upward...

A relaxed spring with spring constant k = 60 N/m is stretched a distance di = 59 cm and held there. A block of mass M = 7 kg is attached to the spring. The spring is then released from rest and contracts, dragging the block across a rough horizontal floor until it stops without passing through...