i'm reposting this here cuz for some reason my post moved to grade k-12 forum..... btw this is a first year University physics question...(adsbygoogle = window.adsbygoogle || []).push({});

this is from my physics assignment... after pulling half of my hair, i still couldn't figure it out...

my answer for part a) is greater and lower

and part b) is same and same...

not sure tho...

thx

4. Part a) A sister has a ball which she throws toward her brother. The ball is thrown with a velocity, v. The brother stands stationary and catches the ball. Now, if instead the brother is running toward his sister when he catches the ball, would he measure a greater or a lower velocity for the incoming ball (relative to himself)? What about if he is moving away from her when he catches the ball? Remember, velocity is relative. ( /1)

4. Part b) The brother is located some distance from his sister. Both are stationary. She shouts at him with a pure tone (say, 400 Hz). He measures that the velocity of sound (emitted from his sister) is 343 m/s when they are both stationary. They try this experiment a second time, but this time the sister runs toward her brother (he is still stationary). He perceives a higher frequency due to the Doppler effect. If he measures the speed of the sound, would he get the same velocity, higher, or lower than when she was stationary? Finally, what if the brother runs toward his sister, who is stationary. As before, she shouts at 400 Hz, and as before, he perceives a higher frequency. When he measures the speed of the sound from his reference frame, what does he get this time, higher, lower, or the same as when they were both stationary? ( /4) (Explain your answers. be careful – this question is tricky) ( /4)

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Doppler effect question

**Physics Forums | Science Articles, Homework Help, Discussion**