The speed of sound is 340.29 meters per second.
Knowing that, we can calculate how high this cliff is by 340.29 * .4
The cliff is 340.29 * .4 = 136.12 meters
==> Object A travels for 60 seconds before Object B starts out.
==> Object A moves at 2 m/s.
==> So Object A has a lead of 120 m when Object B starts out.
==> Object B moves at 3 m/s . . . 1 m/s faster than Object A.
==> So Object B catches up on Object A by 1 m every second.
==> Object B closes up Object A's lead of 120 m in <em>120 seconds</em>.
First of all, let's write the equation of motions on both horizontal (x) and vertical (y) axis. It's a uniform motion on the x-axis, with constant speed

, and an accelerated motion on the y-axis, with initial speed

and acceleration

:


where the negative sign in front of g means the acceleration points towards negative direction of y-axis (downward).
To find the distance from the landing point, we should find first the time at which the projectile hits the ground. This can be found by requiring

Therefore:

which has two solutions:

is the time of the beginning of the motion,

is the time at which the projectile hits the ground.
Now, we can find the distance covered on the horizontal axis during this time, and this is the distance from launching to landing point:
distance
speed = — ————
time
s= 30m
———
6s
the average speed of the marble is 5s/m