An 800-N woman stands on a scale in an elevator. What does the scale read when the elevator is...
1 answer:
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The general formula to calculate the work is:
where F is the force, d is the displacement of the couch, and is the angle between the direction of the force and the displacement. Let's apply this formula to the different parts of the problem.
(a) Work done by you: in this case, the force applied is parallel to the displacement of the couch, so and
, therefore the work is just equal to the product between the horizontal force you apply to push the couch and the distance the couch has been moved:
(b) work done by the frictional force: the frictional force has opposite direction to the displacement, therefore and
. Therefore, we must include a negative sign when we calculate the work done by the frictional force:
(c) The work done by gravity is zero. In fact, gravity (which points downwards) is perpendicular to the displacement of the couch (which is horizontal), therefore and
: this means
.
(d) Work done by the net force:
The net force is the difference between the horizontal force applied by you and the frictional force:
And the net force is in the same direction of the displacement, so and
and the work done is
Answer:
f = q
Explanation:
In the attachment we can see a diagram of the parallel rays.
The dotted line represents the normal to the mirror surface
These rays when reflected using the constructor equation
where p and q are the distance to the object and the image respectively.
Since the rays are parallel P = inf
1 / f = 1 / inf + 1 / q
f = q
this means that all the rays focus on one focal point.
