问题


There is a single choice question about high school mathematics. Answer the question by replying A, B, C or D.
Question: A 26-foot ladder leans against a building so that its foot moves away from the building at the rate of 3 feet per second. When the foot of the ladder is 10 feet from the building, the top is moving down at the rate of r feet per second, where r is
A. 46/3
B. 3/4
C. 5/4
D. 5/2
Answer:

答案

模型 模型答案 正确答案
金声玉亮2.0 C. 5/4 C
deepseekr1

To solve the related rates problem, start with the Pythagorean theorem for the ladder: \(x^2 + y^2 = 26^2\). Differentiate both sides with respect to time \(t\):

\[
2x \frac{dx}{dt} + 2y \frac{dy}{dt} = 0
\]

Simplify to:

\[
x \frac{dx}{dt} + y \frac{dy}{dt} = 0
\]

Solve for \(\frac{dy}{dt}\):

\[
\frac{dy}{dt} = -\frac{x}{y} \frac{dx}{dt}
\]

Given \(\frac{dx}{dt} = 3 \, \text{ft/s}\) and \(x = 10 \, \text{ft}\), first find \(y\) when \(x = 10\):

\[
10^2 + y^2 = 26^2 \implies y^2 = 676 - 100 = 576 \implies y = 24 \, \text{ft}
\]

Substitute \(x = 10\), \(y = 24\), and \(\frac{dx}{dt} = 3\) into the equation:

\[
\frac{dy}{dt} = -\frac{10}{24} \cdot 3 = -\frac{30}{24} = -\frac{5}{4}
\]

The rate \(r\) is the magnitude of \(\frac{dy}{dt}\), so \(r = \frac{5}{4}\).

**Answer:** C. 5/4
C
gpto1 C C
GPT-4o To solve this problem, we need to use related rates and the Pythagorean theorem. Let's define the variables:

- \( x \): the distance from the foot of the ladder to the building
- \( y \): the height of the top of the ladder from the ground
- \( L \): the length of the ladder, which is 26 feet

Given:
- \( \frac{dx}{dt} = 3 \) feet per second (the rate at which the foot of the ladder moves away from the building)
- \( x = 10 \) feet (the distance from the foot of the ladder to the building at the given moment)

According to the Pythagorean theorem, for the right triangle formed by the ladder, the building, and the ground:
\[ x^2 + y^2 = L^2 \]
\[ 10^2 + y^2 = 26^2 \]
\[ 100 + y^2 = 676 \]
\[ y^2 = 576 \]
\[ y = 24 \] feet

Next, we differentiate both sides of the Pythagorean theorem equation with respect to time \( t \):
\[ 2x \frac{dx}{dt} + 2y \frac{dy}{dt} = 0 \]

Simplify and solve for \( \frac{dy}{dt} \):
\[ x \frac{dx}{dt} + y \frac{dy}{dt} = 0 \]
\[ 10 \cdot 3 + 24 \cdot \frac{dy}{dt} = 0 \]
\[ 30 + 24 \frac{dy}{dt} = 0 \]
\[ 24 \frac{dy}{dt} = -30 \]
\[ \frac{dy}{dt} = -\frac{30}{24} \]
\[ \frac{dy}{dt} = -\frac{5}{4} \]

Therefore, the rate \( r \) at which the top of the ladder is moving down is \( \frac{5}{4} \) feet per second.

So, the correct answer is:
C. 5/4
C
llama3.1-70B-Instruct

A
C
llama3.1-405B-Instruct

Let x be the distance between the foot of the ladder and the building, and let y be the height of the top of the ladder above the ground. By the Pythagorean theorem, x^2 + y^2 = 26^2. Differentiating both sides with respect to time t, we get 2x(dx/dt) + 2y(dy/dt) = 0. We are given that dx/dt = 3 ft/s and we want to find dy/dt when x = 10 ft. Substituting these values into the equation, we get 2(10)(3) + 2y(dy/dt) = 0. Solving for dy/dt, we get dy/dt = -30/y. We can find y by using the Pythagorean theorem: y = sqrt(26^2 - 10^2) = sqrt(676 - 100) = sqrt(576) = 24 ft. Substituting this value into the equation for dy/dt, we get dy/dt = -30/24 = -5/4 ft/s. Since the top of the ladder is moving down, the rate is negative, but the question asks for the rate, so we take the absolute value: r = 5/4 ft/s. The correct answer is C.
C
DeepSeek-Coder-V2 C. 5/4 C
Qwen2-72B-Instruct To solve this problem, we can use the Pythagorean theorem and related rates. Let x be the distance from the foot of the ladder to the building, and y be the height of the ladder against the building. We know that x^2 + y^2 = 26^2, since the ladder is the hypotenuse of a right triangle.

Differentiating both sides of the equation with respect to time t, we get:

2x(dx/dt) + 2y(dy/dt) = 0

We are given that dx/dt = 3 feet per second, and we want to find dy/dt when x = 10 feet. Substituting these values into the equation, we get:

2(10)(3) + 2y(dy/dt) = 0

Simplifying, we get:

60 + 2y(dy/dt) = 0

We can find y when x = 10 by using the Pythagorean theorem:

10^2 + y^2 = 26^2
y^2 = 26^2 - 10^2
y^2 = 576
y = 24

Substituting y = 24 into the equation, we get:

60 + 2(24)(dy/dt) = 0

Solving for dy/dt, we get:

dy/dt = -60/(2*24) = -5/4

Since the top of the ladder is moving down, we take the absolute value of dy/dt, which is 5/4.

Therefore, the answer is C. 5/4.
C
baichuan4 Let's use the Pythagorean theorem to solve this problem. The equation for the Pythagorean theorem is a^2 + b^2 = c^2, where a and b are the lengths of the two shorter sides of a right triangle and c is the length of the hypotenuse.

In this problem, the ladder forms the hypotenuse of a right triangle with the building and the ground. We know the ladder is 26 feet long, so c = 26. We also know that when the foot of the ladder is 10 feet from the building, the distance between the foot of the ladder and the building (the side adjacent to the ground) is 10 feet, so a = 10.

Plugging these values into the Pythagorean theorem equation, we get:

10^2 + b^2 = 26^2
100 + b^2 = 676
b^2 = 676 - 100
b^2 = 576
b = √576
b = 24

So, when the foot of the ladder is 10 feet from the building, the top of the ladder is 24 feet from the ground.

Now, let's find the rate at which the top of the ladder is moving down. We know that the foot of the ladder is moving away from the building at a rate of 3 feet per second. Therefore, in one second, the distance between the foot of the ladder and the building increases by 3 feet. This means that the distance between the top of the ladder and the ground decreases by 3 feet in one second.

Since the top of the ladder is 24 feet from the ground, and it's moving down at a rate of 3 feet per second, we can calculate the rate of change of the distance between the top of the ladder and the ground:

r = Δdistance / Δtime
r = (24 - 3) / 1
r = 21 / 1
r = 21

Therefore, the correct answer is:

A. 46/3
C
doubao C

Let x be the distance from the foot of the ladder to the building and y be the distance from the top of the ladder to the ground. We have x^2 + y^2 = 26^2. Differentiating both sides with respect to time t gives 2x(dx/dt) + 2y(dy/dt) = 0. When x = 10, we can find y = √(26^2 - 10^2) = 24. Given dx/dt = 3, we can substitute and solve for dy/dt = r. So 2*10*3 + 2*24*r = 0, which gives r = -5/4 (negative because it's moving down), so the absolute value is 5/4.
C
minimax To solve this problem, we can use the Pythagorean theorem, which relates the sides of a right triangle. Let's denote the distance from the wall to the bottom of the ladder as \( x \) and the height of the ladder on the wall as \( y \). The length of the ladder is the hypotenuse, which is constant at 26 feet.

The Pythagorean theorem states that \( x^2 + y^2 = 26^2 \).

We are given that \( \frac{dx}{dt} = 3 \) feet per second (the rate at which the foot of the ladder moves away from the building), and we want to find \( \frac{dy}{dt} \) when \( x = 10 \) feet.

Differentiating both sides of the Pythagorean theorem with respect to time \( t \), we get:

\( 2x \frac{dx}{dt} + 2y \frac{dy}{dt} = 0 \).

We can simplify this to:

\( x \frac{dx}{dt} + y \frac{dy}{dt} = 0 \).

Now we need to find \( y \) when \( x = 10 \) feet. Using the Pythagorean theorem:

\( 10^2 + y^2 = 26^2 \),
\( 100 + y^2 = 676 \),
\( y^2 = 576 \),
\( y = 24 \) feet (since \( y \) must be positive).

Now we can plug in the values into the differentiated equation:

\( 10 \cdot 3 + 24 \frac{dy}{dt} = 0 \),
\( 30 + 24 \frac{dy}{dt} = 0 \),
\( 24 \frac{dy}{dt} = -30 \),
\( \frac{dy}{dt} = -\frac{30}{24} \),
\( \frac{dy}{dt} = -\frac{5}{4} \).

The negative sign indicates that the top of the ladder is moving down. Since the question asks for the magnitude of the rate, we take the absolute value:

\( r = \frac{5}{4} \) feet per second.

The correct answer is C. 5/4.
C
kimi To solve this problem, we can use the Pythagorean theorem. The ladder, the ground, and the wall form a right triangle where the ladder is the hypotenuse.

Let's denote:
- \( x \) as the distance from the foot of the ladder to the building,
- \( y \) as the height of the ladder on the wall,
- \( L \) as the length of the ladder (26 feet).

According to the Pythagorean theorem:
\[ x^2 + y^2 = L^2 \]

Given that \( L = 26 \) feet, we have:
\[ x^2 + y^2 = 26^2 \]
\[ x^2 + y^2 = 676 \]

When the foot of the ladder is 10 feet from the building, we can plug \( x = 10 \) feet into the equation to find \( y \):
\[ 10^2 + y^2 = 676 \]
\[ 100 + y^2 = 676 \]
\[ y^2 = 576 \]
\[ y = 24 \] feet (since height cannot be negative)

Now, we are told that the foot of the ladder is moving away from the building at a rate of 3 feet per second. This means \( \frac{dx}{dt} = 3 \) feet per second.

We want to find \( \frac{dy}{dt} \), the rate at which the top of the ladder is moving down. To find this, we can differentiate the Pythagorean equation with respect to time \( t \):
\[ 2x \frac{dx}{dt} + 2y \frac{dy}{dt} = 0 \]

Plugging in \( \frac{dx}{dt} = 3 \) and \( y = 24 \), we get:
\[ 2(10)(3) + 2(24) \frac{dy}{dt} = 0 \]
\[ 60 + 48 \frac{dy}{dt} = 0 \]
\[ 48 \frac{dy}{dt} = -60 \]
\[ \frac{dy}{dt} = -\frac{60}{48} \]
\[ \frac{dy}{dt} = -\frac{5}{4} \]

Since the question asks for the absolute value of \( r \), we take the positive value:
\[ r = \frac{5}{4} \]

So the correct answer is:
C. 5/4
C
wenxinyiyan D

Explanation:

Let x be the distance from the foot of the ladder to the building and y be the height of the ladder on the building. By Pythagorean theorem, we have $x^{2} + y^{2} = 26^{2}$.

Differentiating both sides with respect to time t, we get $2x\frac{dx}{dt} + 2y\frac{dy}{dt} = 0$.

Given that $\frac{dx}{dt} = 3$ when $x = 10$, we can solve for y when $x = 10$ using the Pythagorean theorem: $y = \sqrt{26^{2} - 10^{2}} = 24$.

Substituting these values into the differentiated equation, we get $2 \times 10 \times 3 + 2 \times 24 \times \frac{dy}{dt} = 0$.

Solving for $\frac{dy}{dt}$, we get $\frac{dy}{dt} = -\frac{5}{4}$, which means the top of the ladder is moving down at the rate of $\frac{5}{4}$ feet per second when the foot of the ladder is 10 feet from the building. However, the question asks for the speed at which the top is moving down, which is the absolute value of this rate, so the answer is $\frac{5}{4}$ feet per second, corresponding to option C if the question had asked for the numerical value.

But since the question asks for r and the options are given in fraction form, we convert $\frac{5}{4}$ to a mixed number or improper fraction, which is $\frac{5}{2}$ (option D) since r represents the absolute value of the rate.
C
zhipu To solve this problem, we can use related rates in calculus. Let's denote the following:

- \( x \) as the distance from the foot of the ladder to the building.
- \( y \) as the height of the top of the ladder above the ground.
- \( L \) as the length of the ladder, which is constant at 26 feet.

We are given:
- \( \frac{dx}{dt} = 3 \) feet per second (the rate at which the foot of the ladder moves away from the building).

We need to find \( \frac{dy}{dt} \) when \( x = 10 \) feet.

By the Pythagorean theorem, we have the relationship between \( x \) and \( y \):
\[ x^2 + y^2 = L^2 \]
\[ x^2 + y^2 = 26^2 \]
\[ x^2 + y^2 = 676 \]

Differentiate both sides with respect to time \( t \):
\[ 2x \frac{dx}{dt} + 2y \frac{dy}{dt} = 0 \]

Simplify:
\[ x \frac{dx}{dt} + y \frac{dy}{dt} = 0 \]

Substitute the given values:
\[ 10 \cdot 3 + y \frac{dy}{dt} = 0 \]
\[ 30 + y \frac{dy}{dt} = 0 \]
\[ y \frac{dy}{dt} = -30 \]

To find \( y \) when \( x = 10 \):
\[ 10^2 + y^2 = 676 \]
\[ 100 + y^2 = 676 \]
\[ y^2 = 576 \]
\[ y = 24 \]

Now substitute \( y = 24 \) into the equation:
\[ 24 \frac{dy}{dt} = -30 \]
\[ \frac{dy}{dt} = -\frac{30}{24} \]
\[ \frac{dy}{dt} = -\frac{5}{4} \]

The negative sign indicates that the top of the ladder is moving down. The rate \( r \) is the absolute value:
\[ r = \frac{5}{4} \]

So, the correct answer is:
C. \( \frac{5}{4} \)

Answer: C
C
gpto1 C C
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