Mechanical energy Definition and 358 Threads

Homework Statement Derive the Law of Conservation of Mechanical Energy starting from the Work-Energy Theorem. State any assumptions. Homework Equations I'm not really sure where to start with this. Basically how to end up with the equation 0=\DeltaU+\DeltaK The Attempt at a Solution

Hello, Consider a system that is made of a man and a hockey ball on ice (frictionless). Say the man's mass is 80kg and the ball is 0.5kg. At t=0, they are together and they don't move. At an instant the man throw the ball at \frac{10m}{s} against a wall (the ball suffers an elastic...

1. A 1100 kg car at rest at the top of a hill accelerates down the road, reaching a speed of 20 m/s after descending a height of 120 m. What was its total change in mechanical energy (KE plus PEG) as of that moment in Megajoules? 2.KE = 1/2 mv^2 and PEg = mgh 3. I used the above...

Homework Statement A cyclist intends to cycle up a 8.00 hill whose vertical height is 115 . The pedals turn in a circle of diameter 36.0 . 1:Assuming the mass of bicycle plus person is 80.0 , calculate how much work must be done against gravity. 2: If each complete revolution of the...

Homework Statement I have two blocks attached by a string (massless) over a pulley (frictionless, massless). Block 2 (which weighs less than block one) is released and the two blocks meet momentarily at the same height. I have the find the speed at which the meet at that moment. The blocks...

Homework Statement A bird is flying with a speed of 18.0 m/s over water when it accidentally drops a 2.00 kg fish. If the altitude of the bird is 5.40 m and friction is disregarded, what is the speed of the fish when it hits the water? 2. The attempt at a solution I tried v^2=...

Homework Statement Explain what is meant by the conservation of mechanical energy. Write the corresponding equation in detail (in terms of mass speed ect.) a) If friction is not truly negligilble, how would you insert the influence of friction in the equation of the above question? Write...

Homework Statement Just need some direction on the problem. 1. Homework Statement A poorly designed playground slide begins with a straight section and ends with a circular arc. A child starts at point P and slides down both sections of the slide. At some point on the circular arc, the...

Show that a roller coaster with a circular vertical loop. The difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g's-that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this...

Show that a roller coaster with a circular vertical loop. The difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g's-that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this...

Hi, my question is rather simple. Supose you can generate 10 000N, by any means, such as pedaling a bycicle. What calculations should you make to know how much electricity would 10 000 N of force will generate. -Assuming a generator efficiency of 100%, leaving friction aside, etc. An example...

Homework Statement A particle of mass "m" is revolving in a horizontal circle of radius "r" under a centripetal force -k/(r*r), where k is a constant. What is the mechanical energy of the particle. The Attempt at a Solution There are two solutions to the problem I have got. One is mine, the...

what happens to the amplitude if total mechanical energy doubles? i thought, if there was enough mechanical energy in the spring, the amplitude would be at its maximum... like it would have stretched as far as it could, so doubling the total mechanical energy, would only make the periods...

Starting with the equation of motion -kx = ma , it is said that integrating this with respect to x gives the equation for conservation of mechanical energy. Only problem is i don't see how to integrate the right hand side with respect to x...

Hello, I've come up with a simple, imaginary situation that bugs me. Could someone help resolve my confusion? Let's say that a spaceship is traveling through space, and two people- observer 1 and observer 2- are watching it. Both observers can monitor the ship's speed and the amount of fuel in...

I always thought that an electrode is what transforms the mechanical energy of a generator into electrical energy. In a children's book about technology that I was reading yesterday, I saw something that has confused me. The book seemed to imply that the movement of a the wires of a coil...

Homework Statement a pendulum was set up and measurements were made to enable the mechanical energy to be calculated at the start position and the lowest point of the pendulum's swing. The mass of the pendulum bob was determined on an electromic scale, and its diameter was measured using...

Homework Statement The equation below describes a physical situation: 1/2(1.70kg)(3.30m/s)2 + (1.70kg)(9.8m/s2)(2.35m)sin 30º = 1/2(1.70kg)(1.08m/s)2 + 0.320(1.70kg)(9.8m/s2)(2.35)cos 30º Which description best fits the equation? A. A 1.70 kg block slows down while...

I am having problems with this physics problem. Starting from rest a 6.0 kg block slides 2.2m down a rough 30deg incline in 2.0s. find the change in mechanical energy due to friction. answer in J. I know that change in mechanical energy is obtained by E=Ef-Eo or Wnc=(KEf+PEf)-(KEo-PEo)...

What is the significance of negative mechanical eneregy of a body? Eg. electron in 1st orbit of H atom

[SOLVED] Mechanical Energy vs Potential Energy & Kinetic Energy I'm pretty sure I did this one wrong, =( please help clarify? 8. At the Calgary Stampede, you can win a prize if the bell rings when you strike a wooden block with a 10.0-kg hammer. The block is at one end of a lever. The...

FYI: I'm new here but I'm just about done phys 20, just nearing the end of the course. We're working on calculating Work right now. More specifically calculating Mechanical Energy, Kinetic Energy and Potential Energy. I think I've pretty much got most of the equation solved, it's just one last...

Homework Statement A massless string is wrapped around a solid cylinder as shown in the diagram. A block of mass 2kg hangs from a string. When released, the block falls a distance of 82 cm in 2.0 seconds. Calculate the mass using the conservation of mechanical energy. Homework...

Homework Statement A 1200-kg car traveling initially with a speed of 25 m/s in an easterly direction crashes into the rear end of a 9000-kg truck moving in the same direction at 20 m/s. The velocity of the car right after the collision is 18 m/s to the east. (a) What is the velocity of...

[SOLVED] Help! Total mechanical energy question:) Q. Suppose you are standing on a 30 m building and throw a 1 kg rock upwards at 20 m/s. Knowing that total mechanical energy is conserved, calculate the speed of the rock when it hits the ground. Total Mechanical Energy equation: Etotal...

Homework Statement 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...

conservation of mechanical energy ? i found this tricky since i would usually use something like v^2=u^2+2as but i don't have enough variables this time so I don’t even know which direction to go a stone is thrown upwards with u=20m/s. use conservation of mechanical energy to find out how...

Homework Statement A ball of mass 240 g is moving through the air at 20.0m/s with a gravitational potential energy of 70J. With what speed will the ball hit the ground? Homework Equations Eg = mgh Ek = 1/2mv^2 W = mgd The Attempt at a Solution this is what i did: at 0m, potential...

Homework Statement Tarzan and Jane, whose total mass is 130.0 kg, start their swing on a 5.0 m long vine when the vine is at an angle of 30 degrees with the horizontal. At the bottom of the arc, Jane, whose mass is 50.0 kg, releases the vine. What is the maximum height at which Tarzan can...

Homework Statement A 5.5 x 10^4 kg airplane, traveling at an altitude of 9.9 km, has a speed of 260 m/s relative to the ground. Nearing the end of the flight, the plane slows to a speed of 140 m/s while descending to an altitude of 2.1 km. Determine the plane's total loss of mechanical energy...

[SOLVED] Mechanical Energy problem Homework Statement http://img517.imageshack.us/img517/7201/dynamics3oi8.jpg Homework Equations E_{m}=E_k + E_p The Attempt at a Solution I think that the answer to the problem is c), because as the object is moving up, it is slowing down because...

1. Homework Statement During a cold day, you can warm your hands by rubbing them together. Assume the coefficient of kinetic friction between your hands is 0.500, the normal force between your hands is 35.0 N, and that you rub them together at an average relative speed of 35.0 cm/s. (a) What...

[SOLVED] Law of Conservation of Mechanical Energy 1. I was just questioning myself about why LCME won't work under the influence of non-conservational forces Could you go through my attached file I'd originally sent to my physics prof.? I have to wait a week before I meet him and get my...

Homework Statement Figure 8-17 shows one direct path and four indirect paths from point i to point f. Along the direct path and three of the indirect paths, only a conservative force Fc acts on a certain object. Along the fourth indirect path, both Fc and a conservative force Fnc act on the...

A 75-kg trampoline artist jumps vertically upward from the top of a platform with a speed of 5.0 m/s. (a) how fast is he going as he lands on the trampoline 3.0 m below (Fig. 6-23)? (b) If the trampoline behaves like a spring of spring constant 5.2x10^4 N/m, how far does he depress it?

Homework Statement A 50 g ball of clay traveling at speed v_0 hits and sticks to a 1.0 kg block sitting at rest on a frictionless surface. a. What is the speed of the block after the collision? b. Show that the mechanical energy is not conserved in this collision. What percentage of the...

Mechanical energy of a pendulum- I just can't get it! Homework Statement A pendulum of length 140 cm swings with an amplitude of 1.9 cm. Its mechanical energy is 5.7 mJ. What is the mechanical energy of the same pendulum when it swings with an amplitude of 3.7 cm? Homework Equations...

Hi, I just had a question that why the total mechanical energy has to be zero in order for an object to achieve escape velocity? Thanks!

I have no clue in solving this question, can somebody help me? http://tinyurl.com/34ax9f

[SOLVED] Conservation of Mechanical Energy Homework Statement A ride at a generic amusement park starts off by swinging like a simple pendulum until its amplitude becomes so great that it swings completely around. If the diameter of the circle is 30.0 m, what speed must the ship have at...

A projectile has a mass of .750kg and is shot straight up with an initial velocity of 18.0m/s. If the projectile rises to a max height of 11.8m, determine the magnitude of the average force due to air resistance. Can anyone help me with this?

Hi everyone I am a newbie here. I have a question regarding the change in height when two ball collides. I have draw a picture and uploaded the attachment below. Here are some Additional information: Ball A rolls down a frictionless slope and collide with a stationary Ball B. Both balls move...

Homework Statement NOTE: Use the local value of g = 9.809 m/s2 You and your roommate are dragging an exercise machine (mass 56.9 kg) down a 71.2 meter long hall, from the stair landing, where (because of union rules) the UPS driver left it, to your dorm room. The coefficient of friction...

Hi. I really need some help with this problem. I'm a little lost and my head seems ready to explode. Any hints will be appreciated. Homework Statement A softball pitcher rotates a .265 kg ball around a vertical circular path of radius .568 m before releasing it. The pitcher exerts 24.7 N...

I selected two motion problems: 1) Aircraft landing 2) Ball falling onto the gound Using conservation of mechnical energy principles I need to fully expain and justify my reasons why its more suitable than applying Newton's laws of motion. I have already said a) Newton laws of...

MODS close this thread down i figured out the answer myselfHomework Statement A refrigerator has a coefficient of performance of 2.16. Each cycle it absorbs an amount of heat equal to 3.435×104 J from the cold reservoir. i need to find a) the mechanical energy required each cycle to operate...

Homework Statement Hi,I am taking a grade 11 physics correspondance course and I have been stumped for the last few weeks on what they are asking in a particular question. A pendulum was set up and measurements were made to enable the mechanical energy to be calculated at the start...

Homework Statement A block of unknown material weighs 50 N in air and 20 N in water. What is the buoyant force of water? Homework Equations I know how to calculate density etc. I thought the formula to use was -density x V x g but it's not correct. Homework Statement A x Kg mass is...

Homework Statement Students are designing an experiment to demonstrate the conversion of mechanical energy into thermal energy. They have designed the apparatus shown in the figure above. (To see the image, visit http://www.cs.utexas.edu/users/mfkb/Halo/CPL/Physics1998APexam.pdf and check...

Homework Statement A thin rod, of length L and negligible mass, that can pivot about one end to rotate in a vertical circle. A heavy ball of mass m is attached to the other end. The rod is pulled aside through an angle and released. What is the speed of the ball at the lowest point if L =...