Number of neutrons: atomic mass - atomic number
Element X's atomic mass is 79 and its atomic number is 39. Subtract 39 from 79 to find how many neutrons Element X has.
79 - 39 = 40
Element X has 40 neutrons.
The frequency of any repeating event is the number of times it happens in some specified period of time.
The frequency of a wave is the number of cycles, wiggles, compressions etc. that occur in a given time, usually one second.
Answer:
Mass of the car is 1576 kg.
Explanation:
Let the mass of the car be
kg.
Given:
Initial velocity of the car is, 
As the car stops, final velocity of the car is, 
Change in momentum is, 
Now, we know that, momentum is given as the product of mass and velocity.
So, change in momentum is given as:

Therefore, the mass of the car is 1576 kg.
Answer:
a) f₁ = 3.50 m
, b) f₂ = 0.84 m
Explanation:
For this exercise we must use the constructor equation
1 / f = 1 / p + 1 / q
where f is the focal length, p is the distance to the object and q is the distance to the image
a) the distance where the image should be placed is q = 3.50 m and the object is located at infinity p = ∞
1 / f₁ = 1 /∞ + 1 / 3.50
f₁ = 3.50 m
b) in this case the image is at q = -0.600 m and the object p = 0.350 m
1 / f₂ = 1 / 0.350 -1 / 0.600
the negative sign, is because the image is in front of the object
1 / f₂ = 1,1905
f₂ = 1 / 1,1905
f₂ = 0.84 m
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