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In the sport of skeleton a participant jumps onto a sled (known as a skeleton) and proceeds to slidedown an icy track, belly down an head first. In the 2010 Winter Olympics, the track had sixteen turnsand dropped 126 m in elevation from top to bottom. (a) In the absence of non conservative forces, such as friction and air resistance, what would be the speed of a rider at the bottom of the track? Assume that the speed at the beginning of the run is relatively small and can be ignored. (b) In reality, the gold-medal winner (Canadian Jon Montgomery) reached the bottom in one heat with a speed of 40.5 m/s (about 91 mi/h). How much work was done on him and his sled (assuming a total mass of 118 kg) by non conservative forces during this heat?

49.7 $\mathrm{m} / \mathrm{s}$$-4.89 \times 10^{4} \mathrm{J}$

Physics 101 Mechanics

Chapter 6

Work and Energy

Work

Kinetic Energy

Rutgers, The State University of New Jersey

University of Michigan - Ann Arbor

University of Winnipeg

Lectures

03:47

In physics, the kinetic energy of an object is the energy which it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes. The same amount of work is done by the body in decelerating from its current speed to a state of rest. The kinetic energy of a rotating object is the sum of the kinetic energies of the object's parts.

02:08

In physics, work is the transfer of energy by a force acting through a distance. The "work" of a force F on an object that it pushes is defined as the product of the force and the distance through which it moves the object. For example, if a force of 10 newtons (N) acts through a distance of 2 meters (m), then doing 10 joules (J) of work on that object requires exerting a force of 10 N for 2 m. Work is a scalar quantity, meaning that it can be described by a single number-for example, if a force of 3 newtons acts through a distance of 2 meters, then the work done is 6 joules. Work is due to a force acting on a point that is stationary-that is, a point where the force is applied does not move. By Newton's third law, the force of the reaction is equal and opposite to the force of the action, so the point where the force is applied does work on the person applying the force. In the example above, the force of the person pushing the block is 3 N. The force of the block on the person is also 3 N. The difference between the two forces is the work done on the block by the person, which can be calculated as the force of the block times the distance through which it moves, or 3 N × 2 m = 6 J.

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heart E. We can start by saying that he worked on by non conservative forces equals Delta, Ky. E Plus, Delta, P E. And in first Partner are no no non conservative forces. So that would be 1/2 end times these squared minus We not squared, plus M g h. And since the equation has a zero on decided can actually get rid of all the EMS. So zero is equal to 1/2 and the initial velocity is you're so we can get rid of that as well. So we have 1/2 3 squared plus G h. So zero is equal to 1/2 V squared, plus 9.8 times negative 1 26 And when you saw this for me, you would get me is equal to 49 0.7 meter per second. Now when we come to Part B, then us, we start the same way worked on by non conservative forces equals Delta K E plus Delta P E. But now we have to find the work done by non conservative forces since it says that there is friction and there are other resisted forces and we have to figure out the final us. We have to find the working by the non conservative force. So again we start with 1/2 and times V squared minus me not squared plus m g h. And now we're told that the mass is 118 kilograms toward that. The final speed is 40.5 so squared minus zero squared and then plus 118 times 9.8 times negative 1 26 So solving this 40 worked on by non conservative force comes out to be called to for negative 4.98 times 10 to the power for Jules.

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