Originally Posted by

**Mouseman** Question:

A stone is thrown vertically downwards from the top of a cliff. Its height h metres above the beach below at time t seconds is given by.

h= (10- sqrt 5t) (10 + sqrt 5t)

show that acceleration is constant and state its value.

hence find the time when it hits the beach.

The answer is -10 ms-2 however I don't know how to manipulate the above expression.

sqrt 5t should be equal which would give a value of -25 and not 10, which brings me to wonder if the question is supposed to say sqrt 5 times t, would it make a difference? 5t^0.5 however when one multiplies the two and differentiates again would give -25.