Question

The sound level of a train is 121 dB when standing at a distance of 11 m. If you moved back to a distance of 22 m, what would be the sound level there?

A) 127 dB
B) 131 dB
C) 115 dB
D) 111 dB

Answer 1

Answer on Question #47923, Physics, Mechanics — Kinematics — Dynamics The sound level of a train is 121 dB when standing at a distance of 11 m. If you moved back to a distance of 22 m, what would be the sound level there? A) 127 dB B) 131 dB C) 115 dB D) 111 dB

Solution

Changing distance in 2 times leads to change in power of sound in 4 times. In bels change is

$\lg\frac{I}{I_{0}}\approx 0.6$

In decibels - 10 times as in bells,

$0.6\cdot 10=6$

Hence, sound level will be 121-6 = 115 dB.