# Recent content by Cc518

1. ### Interference of sound waves

Sorry, I just assumed that constructive interference means the interference is maximally constructive because I only know how to solve questions when the interference is maximally constructive or maximally destructive. I am not surprised that the answer is wrong because the textbook has lots of...
2. ### Interference of sound waves

Homework Statement Two in-phase loudspeakers, which emit sound in all directions, are sitting side by side. One of them is moved sideways by 3.0 m, then forward by 4.0 m. Afterward, constructive interference is observed 1/4 and 3/4 of the distance between the speakers along the line that joins...
3. ### Energy and momentum conservation

Thank you so much!
4. ### Energy and momentum conservation

Because the object cannot move with the ball from point A to B, the momentum is not conserved?
5. ### Energy and momentum conservation

Oh, I see :smile: Thank you for reply.
6. ### Energy and momentum conservation

Homework Statement An object with a mass of 5kg is placed on a horizontal surface and it has a semi-circular orbit with radius 1m. Its left end is close to a baffle fixed on the ground. A ball with a mass of 1kg is released from the point A by static. The surface and the groove are both smooth...
7. ### Calculating τ by knowing I is proportional to A^2

The factor is less than 1? A0/At=√10^0.8 and At=e-t/τ A0 Then e-t/τ = 1/√10^0.8 t=1, I got τ=1.08s which is twice the answer, 0.54s, though, but I don’t see why I have to divide 1.08 by 2.
8. ### Calculating τ by knowing I is proportional to A^2

Amplitude will decrease by √8dB, right? Then why did you say ?
9. ### Calculating τ by knowing I is proportional to A^2

Thank you for reply:) So does that mean amplitude will decrease by a factor of √10^0.8 ? If so, then e^-t/τ =√10^0.8, t=1, I got τ=1.08s which is not the right answer:( Can any one tell me where I went wrong? Thank you!
10. ### Calculating τ by knowing I is proportional to A^2

Homework Statement A vibrating standing wave on a string radiates a sound wave with intensity proportional to the square of the standing-wave amplitude. When a piano key is struck and held down, so that the string continues to vibrate, the sound level decreases by 8.0 dB in 1.0 s. What is the...
11. ### Object A is stationary while objects B and C are in motion.

OK，thank you so much!
12. ### Object A is stationary while objects B and C are in motion.

Sorry, I still don't understand how WA=0(work done on A equals zero) helps me to understand part b... If we only consider the interactions between A,B and C, excluding the external forces, the total change in kinetic energy is WB+WC=10-5=5J, which makes the total change in potential energy equal...
13. ### Object A is stationary while objects B and C are in motion.

So if we consider A, B and C as one system, the ΔKtot is 14 + 13 =17J. Then the change in potential energy should be -17J since the energy is conserved in an isolated system, am I correct? But the answer says change in potential energy is 5J, I don't understand:sorry:
14. ### Object A is stationary while objects B and C are in motion.

A is stationary which means its velocity doesn't change, therefore its change in kinetic energy is zero, therefore the work done on A is zero
15. ### Object A is stationary while objects B and C are in motion.

The body has to move a distance d