A sound system is designed to produce a 1.0W/m2 sound intensity over the surface of a hemisphere 20 m in radius. What acoustic power is needed from an array of speakers at the center of the sphere?

2513.6 W

Explanation:

Acoustic power = sound intensity × area of hemisphere

Sound intensity = 1 W/m^2

Area of hemisphere = 2πr^2 = 2×3.142×20^2 = 2513.6 m^2

Acoustic power = 1 W/m^2 × 2513.6 m^2 = 2513.6 W

the minimum constant speed at which she can catch the train is 2.7 m/s

given:

acceleration = 0.6

time = 4.5 s

to find:

velocity = ?

formula used:

from 1st kinematic equation we get,

v = u + at

u = initial speed of train = 0 m/s

v = final speed of the train

a = acceleration of the train

t = time

solution:

from 1st kinematic equation we get,

v = u + at

u = initial speed of train = 0 m/s

v = final speed of the train

a = acceleration of the train

t = time

v = 0 + (0.6 × 4.5)

v = 2.7 m/s

the minimum constant speed at which she can catch the train is 2.7 m/s