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.
Answer:
1) ironing a shirt 2) writing on surfaces 3) working of an eraser
The upward force exerted on the board by the support is 530.8 N.
<h3>Upward force exerted on the board by the support</h3>
The sum of the upward forces is equal to sum of downward forces;
total downward forces = 52.8 N + 206 N + 272 N = 530.8 N
downward force = upward force = 530.8 N
Thus, the upward force exerted on the board by the support is 530.8 N.
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The potential difference,electric current ,resistance and new electric current will be 12 V,4 A,3 Ω,2 A.
<h3>What is resistance?</h3>
Resistance is a type of opposition force due to which the flow of current is reduced in the material or wire. Resistance is the enemy of the flow of current.
The energy in terms of the charge and potential difference is;
E= qV
60=5 C × V
V= 12 V
The electric current is found as;
From the ohm's law;
V=IR
12=4 ×R
R=3Ω
If the voltage is constant and the resistance is doubled, then the new electric current is half of the previous condition;
Hence, the potential difference,electric current ,resistance and new electric current will be 12 V,4 A,3 Ω,2 A.
To learn more about the resistance, refer to the link;
brainly.com/question/20708652
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