Answer:

Step-by-step explanation:
It is given that,
A ball of moist clay falls 18.7 m to the ground, s = 18.7 m
It is in contact with the ground for 21.0 ms before stopping,

Let v is the velocity when it reached the ground. Using third equation of motion as :

u = 0 and a = g

v = 19.14 m/s
Let a is the acceleration during time t. It can be calculated as :

Now, u = 19.14 m/s and v = 0




So, the average acceleration of the clay during the time is
. Hence, this is the required solution.