## Physics – mechanics: conservation of energy (9 of 11) sliding

The term “work” has a different meaning in daily life than it does in physics. Only the part of an applied force that is parallel to the motion works on an object in physics. A individual carrying a heavy book, for example, is not doing any work on the book.
Calculate the work done on a box if it is dragged (text5m) along the ground by a force of (F=text20text N) at an angle of (text60)(text°) to the horizontal.
A force of (text10) (textN) is applied to drive a block across a frictionless surface for a rightward displacement of (text5,0) (textm). (text20) (textN) is the weight of the block (vecF g ). Calculate the sum of work performed by the following forces: natural force, weight (vecF g), and applied force.
After a displacement of (text5,0) (textm) to the right, a frictional force of (text10) (textN) slows a moving block to a stop. (text20) (textN) (textN) (textN) (textN) (textN) (textN) (textN) (textN) (textN) (textN) (textN) (textN) (textN) ( Calculate the amount of work performed by the following forces: normal force, weight, and frictional force.

## Normal force on a hill, centripetal force, roller coaster

When more than one force works on an object as it moves and each force does work, how do we measure the total work? What if the powers are in opposition, with one doing good work and the other doing negative? In this case, we measure the net work done by each force and add them up to get the net work (keeping negative works as negative). Alternatively, add the forces together, including the directions, to determine the size and direction of the net force, and then calculate by the distance over which the net force is applied to obtain the net work. You’ll get the same response in either case, which is the net job. The net work informs us how much energy is moved into or out of kinetic energy, causing it to shift (). The work-energy theory sums up everything we’ve spoken about so far: The net work on a system is equal to the change in kinetic energy of the system, or written as an equation:
A person’s legs can exert a force of 1200 N upward on their center of mass during a leap, while the center of mass moves 0.3 m upward. Let’s see what their launch velocity and hang-time are if they weigh 825 N.

### Work energy theorem – kinetic energy, work, force

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The usual force does little function for a block sliding up or down an incline.
The normal force is perpendicular to the surface by definition, and the block slides across it; no part of the normal force is parallel to the motion.
Remember someone who is in an elevator.
The usual force is the force exerted on the individual by the elevator floor.
The person travels upward with the elevator, so the usual force is parallel to the person’s work motion.
When the elevator goes downward, the natural force and negative work are antiparallel to the motion.
Now consider this scenario: what if the elevator slows down as it ascends, so that the usual force is less than the man’s weight?
Is the usual force engaged in positive, negative, or zero work?