# Relative motion problem #7?

Topic: Relative motion problem #7?

May 23, 2019 / By Anna

**Question:**
A passenger on a stopped bus notices that rain is falling vertically just outside the window. When the bus moves with constant velocity, the passenger observes that the falling raindrops are now making an angle of 20 degree with respect to the vertical.
Part A
What is the ratio of the speed of the raindrops to the speed of the bus?
Part B
Find the speed of the raindrops, given that the bus is moving with a speed of 20 m/s.

## Best Answers: Relative motion problem #7?

**Windsor | 3 days ago**

A passenger on a stopped bus notices that rain is falling vertically just outside the window. When the bus moves with constant velocity, the passenger observes that the falling raindrops are now making an angle of 20 degree with respect to the vertical. The direction of the velocity of the raindrops is vertical. The direction of the velocity of the bus is horizontal. R ↓ \ ← 20˚ ↓.. \ ↓ ... \ ↓ …. \ → → → B The line from R to B makes a 20˚ angle with respect to the vertical. The tangent of 20˚ = speed of bus/ speed of rain. Find the speed of the raindrops, given that the bus is moving with a speed of 20 m/s. Tan 20˚ = 20 m/s ÷ speed of rain Speed of rain = 20 ÷ tan 20˚ = 55 m/s According to Pythagorean theorem, Line RB = (20^2 + 55^2)^0.5 =58.5 m/s The actual velocity of the rain drops as the hit the windshield of the bus is 58.5 m/s Part A What is the ratio of the speed of the raindrops to the speed of the bus? tan 20˚ Part B Find the speed of the raindrops, given that the bus is moving with a speed of 20 m/s. 20 ÷ tan 20˚

👍 174 | 👎 3

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**Originally Answered: How do you make a stop motion?**

It would depend on whether your panel has additional "zones" available for more sensors (or you could possibly wire an extra in series with the first one), and whether the power supply can handle it. Motion detectors (unlike many other types of contacts, such as door and window switches) require voltage for their internal electronics to work. Also, there are add-on units that are wireless, even if your base system was hard-wired.

## Readers Answered

**Seymour**

The raindops are falling vertically with some speed "Vy". When the bus starts moving, the raindrops still have the same vertical component of velocity (still "Vy"), but now they also have a horizontal component (relative to the bus) equal to "Vx", whose magnitude is the same as the speed of the bus. When you add the "Vx" vector to the "Vy" vector, you get a velocity vector that's tipped at 20° from the vertical; that means Vx/Vy = tan(20°) Part A: The speed of the raindrops is "Vy" and the speed of the bus is "Vx", so their ratio is "Vy/Vx". But we already said that Vx/Vy = tan(20°), so that means Vy/Vx = 1/tan(20°) Part B: Vy = Vx/tan(20°) = (20m/s)/tan(20°)

👍 70 | 👎 -5

**Nevan Originally Answered: I130 IMMIGRANT PETITION FOR RELATIVE , FIANCEE(E) , OR ORPHAN ...petition approval?**

She's not eligible for adjustment of status because this is not an Immediate relative petition and no visa is immediately available. Is your dad a US citizen? If so, this is an F1 family preference category petition, assuming your sister isn't married, and the minimum wait for that category is 7 years from the time it is filed. It's much longer if she's Filipina or Mexicana. If he's a green card holder, it's an F2b petition, and the wait would be a minimum of 8 years. Since this is not an immediate relative petition, she can't adjust status while in the US since she came here illegally to begin with, even after waiting the 8 years or more for the petition to become valid. She would have to leave the US and get an immigrant visa interview back home. and she'd be turned down initially because she's been living here illegally. as a result of that she is ineligible for any visa for 10 years from the time she actually leaves the US. she might be eligible to apply for a waiver through USCIS, and if she got the waiver, she could return legally at that point and get a green card after she got here. Not an answer you wanted to hear I'm sure, but that's the way it is at the moment. who knows, maybe the law will change while she's waiting.

👍 68 | 👎 -13

**King**

you're on the wonderful suited music. the area might desire to be an identical, so if v(b) is the speed of the boat relative to the river and v(r) is the speed of the river, then {v(b) + v(r)} t(a million) = {v(b) - v(r)} t(2) however the left bracket is basically 10 km/h and the wonderful suited bracket is 6 km/h. From those expressions you will get the speed of the river (and additionally the boat).

👍 66 | 👎 -21

**Humphrey Originally Answered: How do you make a stop motion?**

"what program would you use?" You can use Microsoft Movie Maker, which comes free with your PC. "what are the basic steps?" To take or create it in post? To take the photos: 1) Get your camera on a tripod. This is a MUST! 2) Set up your scene, and your gonna basically move an object in small movements, taking pictures of each movement. 3) It will look better if you can manually change the exposure on your camera, setting it to one exposure (you then avoid 'flickering' videos) Now the way SHE does it in the video is different than normal: 1) She basically put her camera on High-speed burst, or continuous mode, were it takes mult. photos a second. 2) If your camera has 'burst' or 'continuous' mode, just set it to that, and hold down the shutter button for as long as you want to be taking the photos. To create in post: 1) Open all the images in Windows Movie Maker 2) Select all the images (ctrl + a) 3) And drag them down to the timeline 4) Now click on the 'effects' tab under the Edit menu. 5) Scroll down to 'speed up, double' effect 6) Right click on it, and copy it 7) Select all of the images in the timeline (ctrl + a) 8) Now right click on one of the image on the timeline, and right click, and paste 9) Repeat steps 7 & 8 as needed 10) You will notice it gets faster and faster, every time you paste the effect, so do that until you are pleased with the speed. "about how many pictures would it take?" Depends on how long you want your video to be and how smooth to make the frames. In general stop motion videos, 10 FPS (frames per second) is good enough, so 10 x 30 seconds = 300 photos for a 30 second video.

👍 64 | 👎 -29

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