For Newton's second law, the resultant of the forces acting on the book is equal to the product between the mass of the book and its acceleration:
(1)
There are only two forces acting on the book:
- its weight, directed downward: mg
- the force exerted by the hand on the book, of 20 N, directed upward
so, equation (1) becomes
from which we can calculate the book's acceleration, a:
Fortunately, 'force' is a vector. So if you know the strength and direction
of each force, you can easily addum up and find the 'resultant' (net) force.
When we talk in vectors, one newton forward is the negative of
one newton backward. Hold that thought, while I slog through
the complete solution of the problem.
(100 N forward) plus (50 N backward)
= (100 N forward) minus (50 N forward)
= 50 N forward .
That's it.
Is there any part of the solution that's not clear ?
the answer could be (very basic) since options arent given
When light hits the boundary between two different materials, it can undergo both reflection and refraction.
Reflection is the change in the direction of the
wave that strikes the boundary between two materials.<span> It involves a change in the direction of waves when they clash with an obstacle.
Refraction involves the change in the direction of waves as they move from one medium to </span><span><span>another followed</span></span><span> by a change in speed and wavelength (this second medium should have different permitivity for the light to change its initial properties.)</span>
