Answer:
21
Explanation: its actually 20.85 but i guess they round to 21
You need to know the speed and direction of object
Good afternoon.
We have:

The function of velocity:

For
t = 5 s:
Answer:
f = 6.37 Hz, T = 0.157 s
Explanation:
The expression you have is
y = 5 sin (3x - 40t)
this is the equation of a traveling wave, the general form of the expression is
y = A sin (kx - wt)
where A is the amplitude of the motion, k the wave vector and w the angular velocity
Angle velocity and frequency are related
w = 2π f
f = w / 2π
from the equation w = 40 rad / s
f = 40 / 2π
f = 6.37 Hz
frequency and period are related
f = 1 / T
T = 1 / f
T = 1 / 6.37
T = 0.157 s
Answer:
The image will most likely be 20cm in front the mirror since the mirror was placed further 5cm.