Answer:at 21.6 min they were separated by 12 km
Explanation:
We can consider the next diagram
B2------15km/h------->Dock
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B1 at 20km/h
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V
So by the time B1 leaves, being B2 traveling at constant 15km/h and getting to the dock one hour later means it was at 15km from the dock, the other boat, B1 is at a distance at a given time, considering constant speed of 20km/h*t going south, where t is in hours, meanwhile from the dock the B2 is at a distance of (15km-15km/h*t), t=0, when it is 8pm.
Then we have a right triangle and the distance from boat B1 to boat B2, can be measured as the square root of (15-15*t)^2 +(20*t)^2. We are looking for a minimum, then we have to find the derivative with respect to t. This is 5*(25*t-9)/(sqrt(25*t^2-18*t+9)), this derivative is zero at t=9/25=0,36 h = 21.6 min, now to be sure it is a minimum we apply the second derivative criteria that states that if the second derivative at the given critical point is positive it means here we have a minimum, and by calculating the second derivative we find it is 720/(25 t^2 - 18 t + 9)^(3/2) that is positive at t=9/25, then we have our answer. And besides replacing the value of t we get the distance is 12 km.
1. 
Explanation:
We have:
voltage in the primary coil
voltage in the secondary coil
The efficiency of the transformer is 100%: this means that the power in the primary coil and in the secondary coil are equal
where I1 and I2 are the currents in the two coils. Re-arranging the equation, we find
which means that the current in the secondary coil is 14% of the value of the current in the primary coil.
2. 5.7 V
We can solve the problem by using the transformer equation:
where:
Np = 400 is the number of turns in the primary coil
Ns = 19 is the number of turns in the secondary coil
Vp = 120 V is the voltage in the primary coil
Vs = ? is the voltage in the secondary coil
Re-arranging the formula and substituting the numbers, we find:
Answer:
B. Water and sugar.
Explanation:
In the given options water and sugar would be the poor conductor of electricity. Other given options such as water and salt, water and Hcl and water and NaOH are better conductor of electricity because Hcl ,NaOH, salt (Nacl) can break into their ionic form whereas water and sugar will not.
The value of the equivalent resistance for the three resistors connected in series will be the sum of the three values.
To find the answer, we have to know more about the equivalent resistance.
<h3>
What is meant by equivalent resistance?</h3>
- equivalent resistance is the total value of the resistance connected in a circuit.
- If n resistors are connected in series, then the equivalent resistance will be,
- In our question we have three resistors. Thus, the equivalent resistance will be,
Thus, we can conclude that, the value of the equivalent resistance for the three resistors connected in series will be the sum of the three values.
Learn more about the equivalent resistance here:
brainly.com/question/11603204
#SPJ4
Explanation:
Crust...molten
a. Oceanic, iron
b. Continental, silicates
c. less
3. Mantle, Denser
a. Lithosphere
b. Asthenosphere
4. Core
a. elements, rocks
b. liquid, magnetic
(I guess the liquid should come after the is)
Couldn't answer all but wanted to help
