- #1
ujellytek
- 35
- 2
Homework Statement
The rock 'A' is dropped 100m above a river. After 2 seconds, rock 'B' is thrown down from the same height. What initial velocity must be given to rock 'B' so that both rocks hit the river at the exact same time? [No air resistance]
Homework Equations
What is the answer?
The Attempt at a Solution
http://imgur.com/a/59fkU[/B]
Rock A: v1=0 During a 2s drop it travels 19.6m, -4.9(2)^2+100
So the equation for rock A is d=-4.9(t)^2+80.4
When will rock A hit the river? isolate t and I get ~4.0507 seconds
Rock B: v1=? equation is easy to set up: d=-4.9(t)^2+v1(t)+100 (starts 19.6m behind the dropped rock)
Now we sub in the time rock A hits the river: (4.9(4.0507)^2-100) * (4.0507)^-1=v1
This gives me an answer of ~-4.849m/s
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