A stone is thrown horizontally with an initial speed of 10 m/s from the edge of a cliff.A stopwatch measures the stone's trajectory time from the top of the cliff to the bottom to be 4.3 s.What is the height of the cliff if effects of air are negligible?
A)22 m
B)43 m
C)77 m
D)91 m

Question

Quizplus · Accepted Answer

We can use the equation of motion: 
h = ut + 1/2gt^2
where h is the height of the cliff, u is the initial horizontal velocity (which is the same as the final horizontal velocity), g is the acceleration due to gravity (9.8 m/s^2), and t is the time of flight (4.3 s).

Since the initial horizontal velocity is 10 m/s, we have: 
h = 10 m/s x 4.3 s + 1/2 x 9.8 m/s^2 x (4.3 s)^2
h = 43 m + 84.11 m
h = 127.11 m

Therefore, the height of the cliff is 127.11 m, which is closest to choice D (91 m).

A Stone Is Thrown Horizontally with an Initial Speed of 10