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A projectile of mass 0.750 kg is shot straight up with an initial speed of 18.0 m/s. (a) How high would it go if there were no air resistance? (b) If the projectile rises to a maximum height of only 11.8 m, determine the magnitude of the average force due to air resistance.

(a) 16.5 $\mathrm{N}$(b) 2.9 $\mathrm{N}$

Physics 101 Mechanics

Chapter 6

Work and Energy

Work

Kinetic Energy

Cornell University

University of Washington

Hope College

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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for part A. There is no resisted force, so kinetic energy initial plus potential energy initial equals kinetic energy final plus potential energy final. The final. The initial potential energy is Hiroko's. We're starting at the lowest point, and the final kinetic energy is your because it comes momentarily to rest. So we can now start putting some numbers. And so 1/2 M times 18 squared is equal to em times 9.8 times each across out the EMS on both sides, all for each gives me H is equal to 16.5 meters Now. For Part B, there is a non conservative force. So we have worked on by non Conservative Force is equal to Delta Key, plus Delta P E. Now the Delta Ky E is the final kinetic energy zero minus 1/2 M times 18 squared and then plus the final potential energy is M G times 11 point eight meters minus zero. So we have work done by non conservative force is equal to substituting. M is equal to 0.5 kilograms that the work done by non conservative force comes out to be cool to negative 38.49 Negative. 34.8, Jules. And now we know that by definition, work is equal to have times s and we have negative. 34.8 is equal to negative s F times 11.8 or putting negative because of resisting forces opposite to the direction off s solving for F gives me two point 95 Newton's.

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