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  1. Cc518

    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. Cc518

    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. Cc518

    Energy and momentum conservation

    Thank you so much!
  4. Cc518

    Energy and momentum conservation

    Because the object cannot move with the ball from point A to B, the momentum is not conserved?
  5. Cc518

    Energy and momentum conservation

    Oh, I see :smile: Thank you for reply.
  6. Cc518

    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. Cc518

    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. Cc518

    Calculating τ by knowing I is proportional to A^2

    Amplitude will decrease by √8dB, right? Then why did you say ?
  9. Cc518

    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. Cc518

    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. Cc518

    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...
  12. Cc518

    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:
  13. Cc518

    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
  14. Cc518

    Object A is stationary while objects B and C are in motion.

    No work acting on A because no net force exerted on A?
  15. Cc518

    Object A is stationary while objects B and C are in motion.

    Homework Statement Object A is stationary while objects B and C are in motion. Forces from object A do 10 J of work on object B and –5 J of work on object C. Forces from the environment do 4 J of work on object B and 8 J of work on object C. Objects B and C do not interact. What are ΔKtot and...
  16. Cc518

    A father spins his child on a cart

    Oh, yeah. Thank you for the reminder :)
  17. Cc518

    A father spins his child on a cart

    Thank you so much for your help! I really appreciated it!
  18. Cc518

    A father spins his child on a cart

    I think it should be horizontal because if the plane is parallel to the incline of the slope, the object, in this case, the cart, will move up the slope, which is not what happened.
  19. Cc518

    A father spins his child on a cart

    Sorry, I meant mrω2+mgx actually. So is the rotational plane horizontal or is it parallel with the incline of the slope? In other words, does the Tx act as centripetal force or does T act as the centripetal force? Thank you :)
  20. Cc518

    A father spins his child on a cart

    Thank you for reply! I got tention as 179.2n, but the answer I got from other sources is 185n. The fbd they used is different than mine though. https://cloud.smartdraw.com/share.aspx/?pubDocShare=3584F28114431EA1F27BA700C6061213131 They said Tention= mrw^2-mgx Which one is correct?
  21. Cc518

    A father spins his child on a cart

    Homework Statement The father stands at the summit of a conical hill as he spins his 20 kg child around on a 5.0 kg cart with a 2.0-m-long rope. The sides of the hill are inclined at 20 degrees. He keeps the rope parallel to the ground, and friction is negligible. What rope tension will allow...
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