Time to Fall 120m: Solving an SUVAT Problem with a Thrown Weight

[Rumplestiltskin]

Homework Statement

a) How much time does a dropped weight take to fall 120m down a cliff? (I answered this correctly as 4.9s -- √(s/0.5 x g).)
b) What would the time be (in question a) if the weight was thrown downwards at 2.5m/s?

Homework Equations

SUVAT

The Attempt at a Solution

None, apart from a mistaken rearrangement of s = ut + 0.5at^2.

 

[RUber]

I am not familiar with SUVAT, could you provide more detail?
In your equation S = Ut+ .5At^2, the only thing that changes from your first problem is that now u is not 0.
You will end up with a quadratic equation for t. Pick the positive solution.

 

[Rumplestiltskin]

I am not familiar with SUVAT, could you provide more detail?
In your equation S = Ut+ .5At^2, the only thing that changes from your first problem is that now u is not 0.
You will end up with a quadratic equation for t. Pick the positive solution.

How would I isolate t?

 

[SteamKing]

How would I isolate t?

Have you ever solved a quadratic equation?

 

[CWatters]

Perhaps use the Quadratic Formula..

http://www.purplemath.com/modules/quadform.htm

 

[Rumplestiltskin]

Have you ever solved a quadratic equation?

My bad, I was trying to rearrange for t. This crossroad is new to me.

120 = 2.5t + 4.9t^2
4.9t^2 + 2.5t - 120 = 0

A quadratic formula later... 4.7s. Correct! Thanks all.