Answer:

1.69 * 10^(-7) C

Explanation:

We can find this by using the formula for electric potential while making charge the subject of formula:

V = kQ/r

=> Q = (V*r)/k

Where k = Coulumbs constant

V = electric potential

Q = charge

r = distance between doorknob and charged body

From the question,

V = 6 kV = 6000 V

r = (25 + 0.3) cm = 25.3 cm = 253m

Note: Since we assume that the body is a sphere and we know that the charge in a sphere is concentrated in it's center, we add the radius of the sphere to the length of the spark (which tells us the distance between the doorknob and body) to get the distance between the doorknob and the charge.

Hence:

Q = (6000 * 0.253)/(9 * 10^9)

Q = 1.69 * 10^(-7) C

**Answer:**

**Explanation:**

A )

When empty , H₀ length of barge is inside water .

volume of barge inside water = A x H₀

Weight of displaced water = AH₀ x ρ x g

Buoyant force = weight of displaced water = AH₀ ρg

B)

It should balance the weight of barge

Weight = buoyant force

Weight = AH₀ ρg

mass of barge = weight / g

weight / g = AH₀ ρ

= 550 x .55 x 1000

= 302500 kg

**Answer:**

the answer is B

**Explanation:**

we assume that all of these springs have tha same k , the spring constant

elastic energy for the initial system = Ep1=

for the new changed system , the spring constant = k1+k2 = k+k = 2k , but the displacement is also reduced to 0.5 d

so Ep2 =

so the new total Ep stored in the new system is 1/2Ep

hope it helps

Think of a number. Any number. That number is how many thousands of years old a certain rock is. That number is how many times someone has cried in their life. That number is the lucky number of an unlucky man who is yet to realize he is unlucky.

Think of a number. No, think of…numbers.

Picture all of these abstract representations of human thought, all of them forming an imagined pattern, as all patterns are imagined, and picture how those abstractions describe, in specific ways, real moments that exist.

Picture numbers.

There is a woman who lives at 531 Beachwood Street. Her phone number starts with a 3 and ends with a 5. She smiled 18 times yesterday. She is currently thinking of 3 things she needs to do. There are actually 4 things she needs to do. She has forgotten 1 of them.

She touches the doorknob 2 times before committing to its turn. She has 2 eyes. She has 2 hands. She has 2 more chances to make her life what she thinks it should be.

But she doesn’t know it yet.

Think of a number.

Yes! That’s the one! That’s the one that describes an infinity of disparate truths about our disparate universe.

Also, the roads are looking clear.'

**Answer:**

a)

b)

**Explanation:**

First, we need to obtain the linear momentum of the photons of wavelength 350nm.

We are going to use the following formula:

So the linear momentum is given by:

Having the linear momentum of the photon, we can calculate the speed of the hydrogen molecule to have the same momentum, we can use the classic formula for that:

The mass of the hydrogen molecule is given by:

What we've done here is to use the molecular weight of the hydrogen, and covert it kilograms, we had to multiply by two because the hydrogen molecule is found in pairs.

so: