1. This case is affected by the Doppler Effect, the theory invented by an Austrian scientist named Christian Doppler. The hypothesis is that the perceived pitch of a sound changes as the source of the sound moves toward or away from the hearer. When the source of the sound is closer to the hearer, the frequency, or the pitch, gets higher and vice versa. So I think the driver of the ambulance truck will hear a frequency of 3m/s. Since the sound bounces back, 45m/s divided by 15m/s is 3m/s.

2. The sound gets larger as we tap the glass bowl or cup harder. This is because intensity determines loudness. When the force of the sound wave is more intense, the sound grows larger. When we fill water in the bowl or cup, the pitch, or frequency of the sound will get lower. This is due to the fact that when there is water in the bowl or cup, the sound wave will not be able to travel as fast as it did when there was nothing except air, thus influencing the pitch or frequency of the sound.

Q1)As the frequency gets higher the sound gets more louder and the contrast then the result will be it as well. When the siren comes near me then my ear will sense more louder sound and when the siren goes farther then ear will sense smaller sound and the frequecy will get loswer,

Q2)As we tap more harder the sounds gets larger and when we fill with more water then lower sound comes out compared for only a little water.

A1. Well, the doppler effect is the change in preceived pitch that occurs when the source or the receiver of a sound is moving. So when the amblance truck is moving to the wall 90m away, and the sound waves bounces off the wall and comes to the driver, so when the truck gets closer to the wall, eventually the driver will hear more high sounds, I think. So the frequency sound that the driver hear might be 3dB?

A2. When you tap the glass a bit harder, the more energy a sound wave carries, and the intensity increases so the sound will be more loud. And if you fill some water in the cup, the more water you fill, the lower the sound gets.

Q1. 10dB

Q2. If you tap the cup a little harder, the intensity increases and it becomes more louder. When you fill the cup with water, the intensity becomes lower and you will hear lower pitches.

1. I can't understand this question very well. I know that according to the Doppler Effect, the frequency of the sound waves become higher when the source of sound moves towards the hearer, and that the frequency becomes lower when the source of sound moves away from the hearer. But I don't know what happens to the frequency to the driver, because the driver moves in the same direction and in the same speed with the truck.

2. The harder you tap it, the intensity of the sound will be higher. It will carry more energy, and it will be louder. If you fill water in the cup, the pitch of the sound will be lower, because the frequency of the wave will not be as high as it had been in the air in the water.