Question

I would like to know how to find the frequency for part a;specifically, finding the wavelength. The solution given to mestates that to do so, I should do:

2 times length of the string from the post to the pulleyequals wavelength.

I have no idea why this would be so mathematically orotherwise. Please help me.

2.

A student is standing between identical two carts in a laboratory.On each cart there is a string with mass/length 0.049 kg/m. Eachstring is attached to a post on the right. On the left the stringpasses over a pulley. Just below the pulley there is a hanging massM = 2.0 kg. The length of the string from the post to the pulley isL = 0.25 m. Cart A moves to the right with a speed of vA = 10 m/sand cart B is at rest. The speed of sound in air is 345 m/s. Assumethat both strings are excited and oscillate at their fundamentalfrequencies. Note, the acceleration of gravity is g = 9.8m/s2.

a) What is the frequency the student hears from cart B?









b) What is the frequency the student hears from cart A?









c) What beat frequency does the student hear?