2411 Shares

# Help with optimization problem?

Topic: Time and work problem solving methods
June 20, 2019 / By Devan
Question: So I have this optimization problem to do. I tried to get some help from school tutors, they did not know how to do it. "Must be solved by a calculus method" You are at the southernmost point of a circular lake of radius 1 mile. Your plan is to swim a straight course to another point on the shore of the lake, then jog to the northernmost point. You can jog twice as fast as you can swim. Find the route you must take to minimize the time this trip will take and find the time in minutes. I have never seen an optimization like this and I am having a hard time just to set it up. I need to solve this by a CALCULUS method. Please, I need some help.

## Best Answers: Help with optimization problem?

Candi | 6 days ago
Swim to a point on the circle angle 2A (to avoid fractions) round from the southern end. Then jog round the arc (pi - 2A) that remains. (We must work in radians due to differentiation of trig function.) A diagram will show that the straight part = 2*cosA. The time for the whole exercise is T = 2*cosA + (1/2)*(pi - 2A) = 2*cosA + pi/2 - A (The 1/2 at the front of the second term is due to speed being twice as fast.) dT/dA = -2*sinA - 1 For minimum we need dT/dA = 0 ----> sinA = -1/2 ----> A = -30 degrees. 2A = -60 degrees or 60 degrees round the other way. This is where you swim to and then jog the rest.
👍 120 | 👎 6
Did you like the answer? Help with optimization problem? Share with your friends

We found more questions related to the topic: Time and work problem solving methods

1. Okay if cost per square cm = 2 on the top, and 1 for the sides There are one top, one bottom and 4 sides... if X = size of side of square.. and Y = height Cost = 2*2X^2 + 4XY Then you know that 2X^2 + 4XY = 2000 Take the derivative of the cost function with regard to X and set to zero and solve for x... sub into other equation. 2. Define functions for the cost... as it's set.. and then for the area.. then derivative of area function set to zero and sub.
The equation of a line is y = mx + b which ability at (6, 10), the equation is 10 = m(6) + b, or 10 = 6m + b or b = 10 - 6m The x-intercept of this line represents the backside of the triangle. The x-intercept is stumbled on by utilising making y = 0, so y = mx + b 0 = mx + b -b = mx x = -b/m <==== the backside. The y-intercept represents the top of the triangle, stumbled on by utilising making x = 0. y = mx + b y = b <====== the top The formula of the area of the triangle is (a million/2)(base)(top). for this reason, A = (a million/2)(-b/m)(b) A = (a million/2)(-b^2 / m) A = (-a million/2)(b^2/m) yet all of us know that b = 10 - 6m, so A = (-a million/2)( [10 - 6m]^2 / m ) So this would be our area formula, A(m) A(m) = (-a million/2)( [10 - 6m]^2 / m ) we would choose to shrink the area, so we take the spinoff as frequent. A'(m) = (-a million/2) [ 2(10 - 6m)(-6)m - (10 - 6m)^2 (a million) ] / [ m^2 ] A'(m) = (-a million/2) [ (-12m)(10 - 6m) - (10 - 6m)^2 ] / [ m^2 ] A'(m) = (-a million/2) [ (10 - 6m)(-12m - (10 - 6m)) ] / [ m^2 ] A'(m) = (-a million/2) [ (10 - 6m)(-12m - 10 + 6m) ] / [ m^2 ] A'(m) = (-a million/2) [ (10 - 6m)(-6m - 10) ] / [ m^2 ] Now, we make A'(m) = 0. 0 = (-a million/2) [ (10 - 6m)(-6m - 10) ] / [ m^2 ] serious values: 5/3, -5/3 we are able to reject 5/3 by way of fact it incredibly is a favorable slope (the only thank you to form triangles from the 1st quadrant is that if the slope is detrimental). That leaves -5/3, so this tells us the minimum area happens while the slope m = -5/3. to discover the equation of the line, all we would desire to do is discover extreme college the thank you to discover the equation of the line with slope m = = -5/3 and by way of (6, 10). (y2 - y1)/(x2 - x1) = -5/3 (y - 10)/(x - 6) = -5/3 y - 10 = (-5/3)(x - 6) y - 10 = (-5/3)x + 10 y = (-5/3)x + 20

Amanda
The distance that you will swim will be the third leg of an isosceles triangle. Splitting this triangle down the middle gives two congruent triangles with hypotenuse of 1 mile. Let's call the base of each of these triangles 'x'. When you draw it, you'll notice that: x/1 = cosΘ ==> 2x = 2cosΘ. Therefore, the distance that you will swim is 2cosΘ, since there are two triangles. The rate that you'll travel this distance is 'r'. This distance that you'll jog is pi minus the arc-length subtended by the angle pi - 2Θ. (pi - (pi - 2Θ)) = 2Θ The rate that you'll jog this distance is 2r. Now let's use: time = distance / rate. t = 2cosΘ/r + 2Θ/2r. Differentiating yields: t ' = -2sinΘ/r + 1/r. Now let's set our numerator equal to 0. -2sinΘ + 1 = 0 sinΘ = 1/2 Θ = pi/6 t(pi/6) = 2cos(pi/6)/r + 2(pi/6)/2r t(pi/6) = (sqrt3)/r + pi/6r. Since you didn't give the rate, I can't find the exact time in minutes. But notice that the rate at which he swims must be slow. Let's say that it is 1/10 mi/min. Then we'd have: t(pi/6) = (sqrt3)/(1/10) + pi(6/10) t(pi/6) = 17.3 + 5.23 = 22.5. Therefore, the time is reasonable. Essentially, you'll swim a distance of sqrt3 miles to the point on the circle that makes an angle of 2pi/3 with the point that you started from. Then you'll jog a distance of pi/3 around the edge of the lake. Note that the straight-line distance is 2 miles, since radius is 1. The distance that you'll travel, however is pi/3 + sqrt3 = 2.77 miles, which makes sense. Hope this helped.
👍 40 | 👎 -3

Wallace
y-10 = m(x-6) is the equation of all strains via (6,10) the are reduce off is a triangle to grasp the peak and base of this triangle we need to calculate the intersections with x-axis and y-axis. x=zero => y=10-6m y=zero => x=6-10/m so the field is (10-6m)(6-10/m)/two = (60+60-36m-one hundred/m)/two = 60 - 18m - 50/m We need to take the by-product and placed it 0 to discover a minimal = -18 + 50/m² = zero => 50/m² = 18 => m² = 50/18 = 25/nine => m = +- five/three to look if it is a minimal, derive once more -one hundred/m³ > zero if m
👍 35 | 👎 -12