2. How deep should be ocean to enhance physiologically harmful infrasonic waves of 9 Hz frequency? Take 1.5 km/s for the speed of sound in water and nd the minimum and next to minimum depths of the ocean. A Hint: in this case the quantization rule for standing waves is: Z + (N 1) - 5 = L , where N = 1,2,3,... - an integer number. The minimum depth, h1 = Units m v '/ . The next to minimum depth, h2 = Units _ . 3. Why do you think the shape of stringed instruments such as violins, guitars and cellos is curved and reminds a \"hourglass\" figure? How does this shape effect the quality of sound? Please write a small paragraph below (up to 100 words)