3. The human ear can distinguish an echo from the original sound if the delay between them is larger than about 0.0500 seconds. What is the minimum distance between a person and a reflecting wall that will allow the person to hear an echo of her own voice

Explanation:

Let the distance be d . When sound  travels d and is reflected back , it is heard by person as echo . Time taken by sound to travel total of distance 2 d

= 2 d / v where v is velocity of sound.

When this time is .05 s at least , echo will be heard . velocity of sound in air 340 m /s

so for echo to be heard ,

2 d / 340 = .05

d = 340 x .05 / 2

= 8.5 m .

a small object of mass 3.66 g and charge -17.6 µc is suspended motionless above the ground when immersed in a uniform electric field perpendicular to the ground. what are the magnitude and direction of the electric field?

increases it