一根5.5米长的竹竿,能否通过高4米宽3米的门?

बनाया गया: 23 फ़रवरी 2025

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प्रश्न

一根5.5米长的竹竿,能否通过高4米宽3米的门?

विचार

Considering bamboo pole through door

Okay, the question asks whether a 5.5-meter bamboo pole can pass through a door that is 4 meters high and 3 meters wide. This seems like a geometry problem where we want to figure out if the pole can fit, possibly by rotating or using its diagonal orientation. Let me think... we need to check if the pole's length is less than or equal to the door's diagonal when rotated. I'll calculate this to be sure.

Analyzing bamboo pole vs door

Okay, this is a bit tricky! The problem is similar to a classic "ladder problem," where you ask if a long object can be moved through a narrow space. In this case, we have a door that's 4 meters high and 3 meters wide, and a bamboo pole that's 5.5 meters long. If I think about the diagonal of the door, it comes out to about 5 meters, which is shorter than the pole's length. But the pole doesn't need to follow a perfect diagonal — it can be tilted to get through. Let me think on this more!

Exploring bamboo pole orientation

The problem of fitting a 5.5-meter bamboo pole through a 3x4 meter door isn't simple. If the rod stays in the plane of the door, the maximum fitting length is the diagonal of the door, which is about 5 meters. But if the rod is tilted out of the plane, technically it can fit because its projection can be made shorter. So, to determine if the pole can fit, I'd need to calculate its maximum projected length in different orientations for the door.

Reasoned for 29 seconds

उत्तर

答案是可以的。虽然竹竿的长度(5.5米)超过了门的平面对角线(√(3^2+4^2)=5米),但如果适当地将竹竿倾斜出门的平面,就能使其在门平面的投影变短,从而通过门。

详细解释:

  1. 平面投影长度
    设竹竿的实际长度为 L = 5.5米。如果将竹竿以一个角度θ从门的平面倾斜,那么它在门平面上的投影长度为 L·cosθ。

  2. 门的对角线限制
    门的宽为3米,高为4米,其对角线长度为

    32+42=5.\sqrt{3^2+4^2} = 5\text{米}.

    要使竹竿顺利通过门,必须有

    5.5cosθ5.5.5 \cdot \cosθ \le 5.
  3. 求解倾斜角度
    解上述不等式得:

    cosθ55.50.9091,\cosθ \le \frac{5}{5.5} \approx 0.9091,

    对应的θ至少为

    θarccos(0.9091)24.6°.θ \ge \arccos(0.9091) \approx 24.6°.

    也就是说,当竹竿与门平面至少有约24.6°的倾斜时,其在门平面的投影长度就不超过5米。

  4. 合适的平面内旋转
    同时,如果在门平面内调整竹竿的方向,使得它的投影正好沿着门的对角线(水平分量3米,垂直分量4米),那么竹竿的投影就完全符合门的尺寸要求。

因此,通过适当的三维调转(既有门平面内的旋转,又有倾斜出平面的角度),这根5.5米长的竹竿是可以通过高4米、宽3米的门的。

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