Question

A rock is thrown horizontally off a cliff with an initial velocity of 15 m/s. How high was the cliff if the rock lands 22 m from the base of the cliff?

Answer 1

Answer:

22 m

Explanation:

Answer 2

Answer:

cliff height = 10.55 m

Explanation:

Remarks

• This is one of those questions that defies belief. The final vertical velocity is the same as if you just dropped the rock, which is amazing.
• Another amazing fact is that the horizontal speed has no acceleration.
• And  amazing fact number three is the the vertical initial speed is 0.
• And finally, the time taken to go horizontally = time to go vertically.

Solution

Time

So the time taken is d = r * t  

Remember, this formula can only be used when there is no acceleration.

d = 22 meters

r = 15 m/s

t = ?

t = d / r

t = 22 / 15

t = 1.467

Height of the Cliff

vi = 0 (vertially)

a = 9.8 m/s^2

t = 1.467 seconds    The time horizontally and vertically is the same.

d = ?

Formula

d = vi*t + 1/2 a t^2

Solution

d = 0 + 1/2 * 9.8 * 1.467^2

d = 10.55 meters.