Complete question:
A police car is located 50 feet to the side of a straight road. A red car is driving along the road in the direction of the police car and is 130 feet up the road from the location of the police car. The police radar reads that the distance between the police car and the red car is decreasing at a rate of 75 feet per second. How fast is the red car actually traveling along the road.
Answer:
The red car is traveling along the road at 80.356 ft/s
Step-by-step explanation:
Given
Police car is 50 feet side off the road
Red car is 130 feet up the road
Distance between them is decreasing at the rate of 75 feet per sec
Let x be how far the police is off the road.
Let y be how far the red car is up the road.
Let h be the distance between the police and the red car.
This forms a right triangle so we can use the Pythagorean theorem, to solve for h
h² = x² + y²
h² = 50² + 130²
h² = 19400
h = √19400
h = 139.284 ft
Again;
Let dx/dt be how fast the police is traveling toward the road.
Let dy/dt be how fast the red car is traveling along the road.
Let dh/dt be how fast the distance between the police and the car is decreasing.
Recall that, h² = x² + y² (now differentiate with respect to time, t)
2h(dh/dt) = 2x(dx/dt) + 2y(dy/dt)
divide through by 2
h(dh/dt) = x(dx/dt) + y(dy/dt)
since the police car is not, dx/dt = 0
and dy/dt is the how fast is the red car actually traveling along the road
139.284(75) = 50(0) + 130(dy/dt)
10446.3 = 0 + 130(dy/dt)
dy/dt = 10446.3 / 130
dy/dt = 80.356 ft/s
Therefore, the red car is traveling along the road at 80.356 ft/s
THE VOLUME OF A CYLINDER IS
V=π R^2 H
WE HAVE h= 6 in
r=3 in
V= π*9*6=54 π in^3
choice C
A. They are not similar because their corresponding angles are not congruent.
Their angles are not the same.
The 1st triangle is a scalene triangle (a triangle that has 3 unequal sides and angles)
The 2nd triangle is an isosceles triangle (a triangle that has 2 congruent/equal sides and 2 congruent angles)
The total area of the complete lawn is (100-ft x 200-ft) = 20,000 ft².
One half of the lawn is 10,000 ft². That's the limit that the first man
must be careful not to exceed, lest he blindly mow a couple of blades
more than his partner does, and become the laughing stock of the whole
company when the word gets around. 10,000 ft² ... no mas !
When you think about it ... massage it and roll it around in your
mind's eye, and then soon give up and make yourself a sketch ...
you realize that if he starts along the length of the field, then with
a 2-ft cut, the lengths of the strips he cuts will line up like this:
First lap:
(200 - 0) = 200
(100 - 2) = 98
(200 - 2) = 198
(100 - 4) = 96
Second lap:
(200 - 4) = 196
(100 - 6) = 94
(200 - 6) = 194
(100 - 8) = 92
Third lap:
(200 - 8) = 192
(100 - 10) = 90
(200 - 10) = 190
(100 - 12) = 88
These are the lengths of each strip. They're 2-ft wide, so the area
of each one is (2 x the length).
I expected to be able to see a pattern developing, but my brain cells
are too fatigued and I don't see it. So I'll just keep going for another
lap, then add up all the areas and see how close he is:
Fourth lap:
(200 - 12) = 188
(100 - 14) = 86
(200 - 14) = 186
(100 - 16) = 84
So far, after four laps around the yard, the 16 lengths add up to
2,272-ft, for a total area of 4,544-ft². If I kept this up, I'd need to do
at least four more laps ... probably more, because they're getting smaller
all the time, so each lap contributes less area than the last one did.
Hey ! Maybe that's the key to the approximate pattern !
Each lap around the yard mows a 2-ft strip along the length ... twice ...
and a 2-ft strip along the width ... twice. (Approximately.) So the area
that gets mowed around each lap is (2-ft) x (the perimeter of the rectangle),
(approximately), and then the NEXT lap is a rectangle with 4-ft less length
and 4-ft less width.
So now we have rectangles measuring
(200 x 100), (196 x 96), (192 x 92), (188 x 88), (184 x 84) ... etc.
and the areas of their rectangular strips are
1200-ft², 1168-ft², 1136-ft², 1104-ft², 1072-ft² ... etc.
==> I see that the areas are decreasing by 32-ft² each lap.
So the next few laps are
1040-ft², 1008-ft², 976-ft², 944-ft², 912-ft² ... etc.
How much area do we have now:
After 9 laps, Area = 9,648-ft²
After 10 laps, Area = 10,560-ft².
And there you are ... Somewhere during the 10th lap, he'll need to
stop and call the company surveyor, to come out, measure up, walk
in front of the mower, and put down a yellow chalk-line exactly where
the total becomes 10,000-ft².
There must still be an easier way to do it. For now, however, I'll leave it
there, and go with my answer of: During the 10th lap.
