The cliff is 12.71m tall.
Why?
Before solving the problem, we must remember that the phone was dropped, it means that there is no initial velocity, also, the acceleration acting on the phone is the acceleration due to gravity.
So, to find how tall is the cliff, we can use the following equations:
[tex]y=y_o+v_o*t-\frac{1}{2}g*t^{2}\\\\v_f=v_o+g*t[/tex]
[tex]t=\frac{v_f}{g} \\\\t=\frac{-15.75\frac{m}{s}}{-9.81\frac{m}{s^{2}}}=1.61s[/tex]
Now that we know the time, we can calculate how tall is the cliff:
[tex]y=y_o+v_o*t+\frac{1}{2}g*t^{2}\\\\y=0+0*1.61s-\frac{1}{2}*(-9.81\frac{m}{s^{2}})*(1.61s)^{2}\\\\y=12.71m[/tex]
Hence, we have that the cliff is 12.71m tall.
Have a nice day!
