Conservation of energy Definition and 1000 Threads

Homework Statement A 2.5 kg block of ice at a temperature of zero degrees celcius and an initial speed of 5.7 m/s slides across a level floor. If 3.3 x 105 J are required to melt 1 kg of ice, how much ice melts, assuming that the initial kinetic energy of the ice block is entirely converted to...

Could some one please explain to me why energy is conserved in a roller coaster car on a frictionless roller coaster car ride when the conservation law says that energy will only be conserved when their are no outside forces applied. Isnt the force supplied by the rails to change the cars...

Homework Statement Show that on 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 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...

Hmm. This is another thing I'm unsure abt. When some mechanical energy is converted to internal energy, can we still say that energy is conserved? Can the internal energy be negative? Thanks for answering my qns :)

Homework Statement A 0.570-{\rm kg} wood block is firmly attached to a very light horizontal spring(k=180 N/m). It is noted that the block-spring system, when compressed 4.4 cm and released, stretches out 1.7 cm beyond the equilibrium position before stopping and turning back. What is the...

Two snow-covered peaks at elevations of 3500 m and 3400 m are separated by a valley. A ski-run having a total length of 3000 m extends from the top of the higher peak to the top of the lower one. A skier starts from rest on the higher peak. With what speed will the skier arrive at the topof...

[b]1. A bowling ball is hanging by a wire from the ceiling, and is swinging back and forth... [b]2. At what position(s) does it have the least speed?, greatest speed?, least kinetic energy and why?, greatest kinetic energy and why?, greatest mechanical energy and why? The Attempt...

Homework Statement The cable of the 1800 kg elevator in Figure 8-56 snaps when the elevator is at rest at the first floor, where the cab bottom is a distance d = 3.7 m above a cushioning spring whose spring constant is k = 0.15 MN/m. A safety device clamps the elevator against guide rails so...

[FONT="Century Gothic"][SIZE="1"] Homework Statement A pendulum consists of a 4.0 kg stone swinging on a 3.2 m string of negligible mass. The stone has a speed of 7.7 m/s when it passes its lowest point. Homework Equations (a) What is the speed when the string is at 62° to the vertical...

A cart, initially at rest, slides down a frictionless ramp onto a horizontal frictionless surface which is a distance h below the original position of the cart. It then collides with the free end of a relaxed horizontal spring, the other end of which is fixed to a wall. As a result the spring...

Homework Statement A parachutist with mass m = 70 kg jumps from an airplane traveling at a speed v = 100 km/h at a height H = 2500 m and lands with a speed vf = 5.00 m/s. Use the “conservation of energy strategy” to calculate the change in internal energy of the system from just after the...

Homework Statement A 75.0 kg mass sits on an inclined plane, and a rope passing over a pulley at the top connects it to a hanging 125 kg mass. The pulley is frictionless and its mass is negligible. The coefficient of friction between the 75.0 kg block and the plane is 0.143. The system is...

Alright, so I'm a little stuck on the last bit of this problem: The cable of the 1,800 kg elevator cab snaps when the cab is at rest at the first floor, where the cab bottom is a distance d = 3.7 m above a cushioning spring whose spring constant is k = 0.15 MN/m. A safety device clamps the cab...

Homework Statement why is the gravitational potential energy of a ball equal to its kinetic energy Homework Equations KE=PE The Attempt at a Solution im really not sure, i think its because energy is conserved but i don't know why that is either

Homework Statement How does a roller coaster demonstrate the law of conservation of energy by the transfer of potential energy to kinetic energy Homework Equations KE=PE The Attempt at a Solution i believe that as the roller coaster descends down the hill the potential energy...

Homework Statement a moving train collides with a train that is not moving, and the trains use their springy bumpers to bounce off of each other without damage. Assume diff masses for train A and B. Identify your isolated system, solve for the final velocity of EACH train in terms of INITIAL...

Homework Statement The sliding block has a mass of 0.800 kg, the counterweight has a mass of 0.460 kg, and the pulley is a hollow cylinder with a mass of 0.350 kg, an inner radius of 0.020 m, and an outer radius of 0.030 m. The coefficient of kinetic friction between the block and the...

Homework Statement An alpha particle with kinetic energy 10.5 MeV makes a collision with lead nucleus, but it is not "aimed" at the center of the lead nucleus, and has an initial nonzero angular momentum (with respect to the stationary lead nucleus) of magnitude L = p_0 b, where p_0 is the...

Homework Statement Homework Equations Rotational Kinetic Energy = 1/2*I*w^2 The Attempt at a Solution I was just wondering if someone explain to me why the potential energy is MgL/2 ? Is this not the same for the torque from gravity?

Homework Statement A climber's gravitational potential energy increases from 14000 J to 21 000 J while climbing a cliff. She expends 18 000 J of energy during this activity. What is the efficiency of this process? Homework Equations Efficiency= useful output/ total input Total...

Conservation of Energy Problem: Where did it go?? Imagine I shoot a boulder vertically into the air with a massive cannon. Its kinetic energy is converted into gravitational potential, and into KE of air particles (air resistance). So at m metres above the ground, mgh is the Potential energy...

Homework Statement A skier of mass 55.0 kg slides down a slope 11.7 m long, inclined at an angle θ to the horizontal. The magnitude of kinetic friction is 41.5 N. The skier's initial speed is 65.7 cm/s (0.657 m/s) and the speed at the bottom of the slope is 7.19 m/s. Determine the angle θ from...

Hi everybody! So this is my first time using this forum. I'm currently taking AP Physics C: Mechanics in high school and I have some questions concerning Potential Energy and Conservation of Energy. Thanks for taking the time to help me! Homework Statement 32. A 4.0-lb block slides...

Homework Statement A particle sits at the top of a sphere of fixed radius a. It is given a tiny nudge and begins to slide down the frictionless surface of the sphere. My attachment won't work so I'll try and explain. Theta, \theta, is the angle which the particle makes with the vertical axis...

Homework Statement An atom of mass M is initially at rest, in its ground state. A moving (nonrelativistic) electron of mass m_e collides with the atom. The atom+electron system can exist in an excited state in which the electron is absorbed into the atom. The excited state has an extra...

Homework Statement 1. A block mass m is pushed up against a spring, compressing it a distance x, and the block is then released. The spring projects the block along a frictionless horizontal surface, giving the block a speed v. The same spring projects a second block of mass 4m, giving it a...

Homework Statement A red car and a blue car collide at an in intersection. Prior to the collision the red car with mass 1000kg was heading North at 15m/s. The blue car with mass 1500 kg was heading East at 20m/s. The collision is completely inelastic with the cars sticking together and...

1. Tarzan and Jane, whose total mass is 115.0 kg, start their swing on a 5.0 m long vine when the vine is at an angle of 30.0° 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 land on a branch after his...

Dear All, Suppose we have a movable inclined plane (initially at rest) which has height h (if we attach wheels, then it should be movable) and assume that there is no friction anywhere. If a block travels with speed V towards the plane and goes up to the distance h, I wonder ; Is mechanical...

Homework Statement "Show how conservation of energy (with only gravitational potential energy and kinetic energy) can be gotten from Newton's Laws. This was the question that was asked of me, and sorry for the wording not being terribly precise. Homework Equations I am not exactly...

Homework Statement A man lifted a full keg of beer (mas 62kg) to a height of about 2m 676 times in 6 hours. Assuming that work was done only as the keg was going up, estimate how many such kegs of beer he would have to drink to reimburse his energy expenditure. (1 L of beer is approximately...

During a rockslide, a 340 kg rock slides from rest down a hillside that is 500 m long and 300 m high. The coefficient of kinetic friction between the rock and the hill surface is 0.24. (a) If the gravitational potential energy U of the rock-Earth system is set to zero at the bottom of the...

Homework Statement 1. A roller coaster car of mass 1500kg starts a distance H =23m above the bottom of a lopp 15m in diameter. If friction is negligible, the downward force of the rails on the car when it is upside down at the top of the loop is ? 2. Lou is trying to kill mice by swinging a...

A 28 kg bear slides, from rest, 6 m down a lodgepole pine tree, moving with a speed of 5.9 m/s just before hitting the ground. (a) What change occurs in the gravitational potential energy of the bear-Earth system during the slide? (b) What is the kinetic energy of the bear just before...

Homework Statement A child's toy consists of a block that attaches to a table with a suction cup, a spring connected to that block, a ball, and a launching ramp. The spring has a spring constant k, the ball has a mass m, and the ramp rises a height y above the table, the surface of which is...

Homework Statement A roller coaster car has a mass of 800kg. It is released from the top of the hill A and moves without friction down the track. Determine the minimum exit velocity vD at ground level so that the car travels around both the circular loops (Loop B - Radius= 10m, Loop C -...

Homework Statement Two stones are thrown with the same initial speed at the same instant from the roof of a building. One stone is thrown at an angle of 30 degree above the horizontal; the other is thrown horizontally.(Neglect air resistance.), which of the following is true: (a)The...

Homework Statement A cylinder is released from rest from the top of an incline of inclination 'n' and length "L". If the cylinder rolls without slipping what will be its speed at the bottom?The Attempt at a Solution This is an example question from my textbook! The solution has been given. It...

Homework Statement A 2300g mass starts from rest and slides a distance L down a frictionless 26 degree incline, where it contacts an unstressed 34cm long spring of negligible mass as shown in the figure. The mass slides an additional 17cm as it is brought momentarily to rest by compressing the...

Homework Statement A 6kg block slides on a horizontal frictionless surface with a speed of 1.2 m/s. It is brought momentarily to rest when it hits a bumper that compresses a spring. Heres a picture of the problem. When I was doing this problem, I thought there were only two different...

Homework Statement a block is held 1.3m above a spring and is dropped.The spring compresses 6cm before sending the ball into the air. How fast is the ball going when it hits the spring? What is the spring constant? How high in the air does the ball go after hitting the spring? Homework...

Homework Statement problem is here http://img151.imageshack.us/img151/1675/question7ql6.th.jpg http://g.imageshack.us/thpix.php Homework Equations The Attempt at a Solution for the #7 part http://img232.imageshack.us/img232/9079/problem7answerqq9.th.jpg http://g.imageshack.us/thpix.php...

Homework Statement attached Homework Equations equation in the problem k = 898 N/m m = 90.7g = .0907kg d = 27 inch = .6558m g = 9.8 m/s The Attempt at a Solution h = [(898n/m)/(2)(.0907kg)(9.8m/s)](.6558m)^2 - (.6558) that is for the H. when computing this is got...

Homework Statement A simple pendulum whose length is L=2 meters has a mass of m=2kg. When the angle between the pendulum and the vertical is 35 degrees, it has a speed of 1.2 m/s. Find the pendulum's speed when the pendulum is at its lowest height. Homework Equations K = 0.5mv2 U = mgh...

Homework Statement 2 boxes are connected by a massless rope. the system is frictionless m1 = 3kg m2 = 5kg http://img388.imageshack.us/img388/2033/problemwr4.jpg Find m1's speed when it is 1.8 m above the ground. Homework Equations K = 0.5mv^2 U = mg delta y The Attempt at a Solution...

Homework Statement A roller coaster car starts from rest and rolls down a frictionless track, reaching Vf ( final speed) at the bottom. if you want the car to go two times as fast at the bottom by what fator must you increase the height of the track Homework Equations KE=1/2mv^2...

Homework Statement A skier of mass m starts from rest at the top of a solid sphere of radius r and slides down its frictionless surface. At what angle (theta) will the skier leave the sphere? And if friction were present, would the skier fly off at a greater or lesser angle? Homework...

Homework Statement Okay, I have a total mass of 0.255 of a stone that strikes the ground. Assuming that the stone is initially at rest when it begins falling, how high must the stone be above the ground for the energy of the stone and ground to increase by 2450 J? Homework Equations...

Conservation of Energy--please help me! Homework Statement A block is pushed against the spring with spring constant 5.7 kN/m (located on the left-hand side of the track) and compresses the spring a distance 4.6 cm from its equilibrium position. The block starts at rest, is accelerated by the...

hello, I been doing physics homework and I came across this problem that i think i know how to do but for some reason i cannot get the right answer! any help will be very appreciated thanks a lot:) Homework Statement The highest waterfall in Canada is the Della Falls in B.C. with a...