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A bicyclist rides 5.0 km due east, while the resistive force from the air has a magnitude of 3.0 N and points due west. The rider then turns around and rides 5.0 km due west, back to her starting point. The resistive force from the air on the return trip has a magnitude of 3.0 N and points due east. (a) Find the work done by the resistive force during the round trip. (b) Based on your answer to part (a), is the resistive force a conservative force? Explain.

$-3.0 \times 10^{4} J$the resistive force isn ot a conservative force

Physics 101 Mechanics

Chapter 6

Work and Energy

Work

Kinetic Energy

Rutgers, The State University of New Jersey

Hope College

University of Sheffield

McMaster University

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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So let's ah, consider the first part of the question. You have a person who's driving their bike or riding their bike towards the east, so this is the direction off their speed. But the direction of the resistant force is in the opposite direction so we can start working out the worked on by friction. And that would be cool, too negative f s because the force of friction is opposite to the direction of motion. And that would be negative. Three points year old times 5000 mutant. And that comes out as a 5000 meters that comes out as negative 15,000 jewels. Now, this was, uh, going east. Now, after a while, the writer turned around, and now the writer is going west. And what happens to the force of friction now is that the force of friction is pointing in the opposite direction. So let's just say that this was work done by friction in the first case. And now let's find the work done by friction in the second case. Well, the force of friction and displacement are still in opposite directions, so it would still be negative three times 5000 which comes out as negative. 1500 negative 15,000 do. Now let's talk about the network down. So the net work done by resistant force. So we found that in the first case start was negative 15,000 jewels. In the second case, it was also a negative 15,000 jewels. So the network done by the resistor force is negative 30,000 jewels. And we would say that resisted force is non conservative, non conservative because network is not going to zero for the resistance for a conservative forth, the network, done in a round trip should be zero.

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