Answer:
Explanation:
Given:
length of ladder 
weight of ladder 
position of firefighter 
weight of firefighter 
angle of ladder 
Unknown:
force of the wall on the ladder 
force of friction on base of ladder 
normal force on base of ladder 
From the free body diagram of the sketch you get 3 equations:

Solving the equations gives:

a)

b)

c) Using the result from b and solving for 

Answer:
The sum of positive and negative charges in a unit of Al2O3 equals zero.
Aluminium has a charge of +3 while Oxygen has a charge of -2 on each ion.
Al203 has 2 Al atoms and 3 O atoms.
Charge on Al2O3 = 2(charge on Al ion) + 3(charge on O ion)
= 2(3) + 3(-2)
= 6 - 6
= 0
Explanation:
Aluminium has 3 electrons in the outermost shell and has the tendency to lose those 3 electrons to form a positive ion and have a complete outermost shell.
Whereas, Oxygen has 6 electrons in the outermost and has the tendency to accept two more electrons to form a negative ion and have a complete outermost shell.
PART A)
By Snell's law we know that

here we know that



now from above equation we have


so it will refract by angle 39.3 degree
PART B)
Here as we can see that image formed on the other side of lens
So it is a real and inverted image
Also we can see that size of image is lesser than the size of object here
Here we can use concave mirror to form same type of real and inverted image
PART C)
As per the mirror formula we know that



so image will form at 30 cm from mirror
it is virtual image and smaller in size