Answer:
D. a person pulling a sled.
Explanation:
contact force only occurs when something directly comes in contact with another object.
a. is wrong because that is called magnetic force.
b. gravitational force
c. is an electrical force
Answer:
C
Explanation:
Magnitude of any quantity is the measurable value of the quantity. While the direction of the given quantity is the specific pointing direction of position or the angle at which it move.
The magnitude of the vector described below? 13 m/s to the east will be 13 m/s
While the direction will be eastward.
Therefore, the magnitude is 13 m/s
The correct answer is option C
<span>E=hc/wav. len
E = (6.62 x 10^-34 x 3 x 10^8)/0.0275 x 10^-9
E = 7.22182 x 10^-15 J
To convert to eV divide by 1.6 x 10^-19
E = 7.22182 x 10^-15/1.6 x 10^-19 eV
E =45.36 x 10^3 eV
Th energy, E, of a single x-ray photon in eV is = 45.36keV.
Number of photons, n = total energy/ energy of photon
n = 3.85 x 10^-6/7.22182 x 10^-15
n = 5.33 x 10^8 photons </span>
It's Photoelectric Effect, I just a test with this same question. I am not good for explaining exactly how, but I was right.
Answer: 
Explanation:
The density 
of a material is given by:
(1)
Where:
is the mass of the cube
is the volume of the cube
Now, the volume of a cube is equal to the length 
of its edge to the power of 3:
(2)
If we know 
, the volume of this cube is:
(3)
Substituting (3) in (1):
(4)
This is the density of the cube
