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The hammer throw is a track-and-field event in which a 7.3-kg ball (the “hammer”), starting from rest, is whirled around in a circle several times and released. It then moves upward on the familiar curvingpath of projectile motion. In one throw, the hammer is given a speed of 29 m/s. For comparison, a .22 caliber bullet has a mass of 2.6 g and, starting from rest, exits the barrel of a gun at a speed of 410 m/s. Determine the work done to launch the motion of (a) the hammer and (b) the bullet.

a. $=3.07 \times 10^{3} J$b. $=218 J$

Physics 101 Mechanics

Chapter 6

Work and Energy

Work

Kinetic Energy

University of Michigan - Ann Arbor

Simon Fraser University

Hope College

University of Sheffield

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 we will use the idea that work is equal to Delta K. So in part A, we're talking about the hammer. So work would be equal to 1/2 m times V squared minus V initial squared or be not squared and the pass off the hammer, a 7.3 kilograms. The final speed off the hammer is 29 lida per second squared, so meter per second and then the initial speed A zero. So the work done on the hammer comes out to be 0.3 points. You're seven times 10 to the power. Three jewels are talking about the bullet. Same concept. Work is equal to 1/2 em B squared minus. We not squared. And now the mass off the bullet is just 2.6 grams. But we have to change that two kilograms or divide by 1000 and the final speed off the bullet is 410 meter per second, and the initial speed is zero. And when you saw that, it comes out as 218 Julie

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