As we know that mass of the box is given as
m = 9.5 kg
acceleration of the box is given as

so by Newton's II law we can say

now we can substitute all the values in it


So it required 9.5 N force to slide it
Answer:
t=4.86s
Explanation:
To find the wavelength you use the following formula:

v: speed of sound = 343m/s
f: frequency = 400Hz
λ: wavelength of the sound
By doing λ the subject of the formula and replacing the values of f and v you obtain:

Now, to calculate the time that sound takes to reach the last row you use:

t: time
d: distance to the last row = 1947m

hence, the time is 4.86s
True because we have limited amount if it