physics question

2007-06-06 2:12 am

1) A tube of length 70 cm open at both ends is found to resonate with a tuning fork of frequency 256 Hz. Calculate the wavelength of the vibration in the tube.

2) A 7kg object is weighed by a spring balance in an elevator. What is the reading of the balance when the elevator is:
a) at rest
b) ascending & decending with uniform speed
c) moving upwards with uniform acceleration 1 m/s2
d) moving downwards with uniform acceleration 1 m/s2
(please give answer with explanation, many thanks)

回答 (1)

用戶40379

2007-06-06 2:54 am

✔ 最佳答案

1) A tube of length 70 cm open at both ends is found to resonate with a tuning fork of frequency 256 Hz. Calculate the wavelength of the vibration in the tube.
在開管(open at both ends)，它的基音波長等於兩倍的管長。所以
λ = 2x0.7
= 1.4m

2) A 7kg object is weighed by a spring balance in an elevator. What is the reading of the balance when the elevator is:
a) at rest
w = mg
= 7x10
= 70N
b) ascending & decending with uniform speed
w = mg
= 7x10
= 70N
c) moving upwards with uniform acceleration 1 m/s2
w = m(g + a)
= 7(10 + 1)
= 77N
d) moving downwards with uniform acceleration 1 m/s2
w = m(g - a)
= 7(10 - 1)
= 63N

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