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On a still day, rain falls straight down at 9 m/s…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
On a still day, rain falls straight down at . Nikhil cycles along a straight road at .
- At what angle to the vertical does the rain seem to fall, to him? How should he hold his umbrella?
- How fast does the rain hit his umbrella?
- The next day, a wind blows the rain forward along the road at , in the direction he rides. How does the rain seem to fall now?
Need a reminder? The key ideaShow
What you see is the rain's velocity relative to you: . Tilt the umbrella towards where the rain seems to come from.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Relative velocity. : down, and backwards, towards his face.
Step 2. Angle. , so from the vertical. He tilts the umbrella forward by .
Step 3. Speed. .
Step 4. With the wind. The rain now moves forward at , just as he does. Relative to him it has no forward or backward part, so it seems to fall straight down at . He holds the umbrella upright.
Answer: (a) from the vertical, from the front: he tilts the umbrella forward. (b) . (c) Straight down.
Watch out. In (c), the rain really slants forward, but to Nikhil it falls straight. What you see always depends on how you move.
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