Answer:
The height from which the rock was thrown is 1.92 m
Solution:
As per the question:
Speed with which the rock is thrown, v = 12.0 m/s
Horizontal distance traveled by the rock before it hits the ground, d = 15.5 m
Launch angle,

Now,
To calculate the height, h from which the rock was thrown:
First, since we consider the horizontal motion in the trajectory of the rock, thus the time taken is given by:


Now,
The height from which the rock was thrown is given by the kinematic eqn, acceleration in the horizontal direction is zero:

