Answer:
Explanation:
Force between charge is given by the following expression
F = k Q₁ Q₂ / R² , k = 9 x 10⁹ , Q₁ and Q₂ are charges , R is distance between charges .
Putting the given values ,
.85 = 9 x 10⁹ x 7.1 x 10⁻⁶ x Q₂ / 5.4²
Q₂ = .85 x 5.4² / (9 x 10⁹ x 7.1 x 10⁻⁶ )
= .38788 x 10⁻³ C .
= 387.88 x 10⁻⁶ C .
Complete Question
A parallel plate capacitor creates a uniform electric field of 5 x 10^4 N/C and its plates are separated by 2 x 10^{-3}'m. A proton is placed at rest next to the positive plate and then released and moves toward the negative plate. When the proton arrives at the negative plate, what is its speed?
Answer:

Explanation:
From the question we are told that:
Electric field 
Distance 
At negative plate
Generally the equation for Velocity is mathematically given by

Therefore




Answer : The energy of one photon of hydrogen atom is, 
Explanation :
First we have to calculate the wavelength of hydrogen atom.
Using Rydberg's Equation:

Where,
= Wavelength of radiation
= Rydberg's Constant = 10973731.6 m⁻¹
= Higher energy level = 3
= Lower energy level = 2
Putting the values, in above equation, we get:


Now we have to calculate the energy.

where,
h = Planck's constant = 
c = speed of light = 
= wavelength = 
Putting the values, in this formula, we get:


Therefore, the energy of one photon of hydrogen atom is, 
If net charge on one object is doubled, then electric force will also get double. It is because they are directly proportional to each other.
Hope this helps!
The final velocity of the two pucks is -5 m/s
Explanation:
We can solve the problem by using the law of conservation of momentum.
In fact, in absence of external force, the total momentum of the two pucks before and after the collision must be conserved - so we can write:

where
is the mass of each puck
is the initial velocity of the 1st puck
is the initial velocity of the 2nd puck
v is the final velocity of the two pucks sticking together
Re-arranging the equation and solving for v, we find:

Learn more about momentum:
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