# Physics

A woman on a bridge 90.0m high sees a raft floating at a constant sped on the river below. She drops a stone from rest in an attempt to hit the raft. The stone is released when the raft has 6.00m more to travel before passing under the bridge. The stone hits the water 2.00m in front of the raft. Find the speed of the raft.

I made a table with Y:-90m, A:9.8m/s^2, Vo: 0
So since y+ Vot+1/2at^2
90= 0+ ½(9.8) t^2
T+ 4.29

I figured the raft moves 4.00m.

So

4.00m/4.49s =.89 m/s

But the answer in the back of the book is .932m/s

What did I do wrong?

1. 👍
2. 👎
3. 👁
1. What you did wrong was forget that you had (correctly) calculated the time to reach the water as 4.29 s. You then changed it to 4.49 s.

The raft moves 4 m in the time it takes the stone to fall 90 m. That time T is given by the equation
(g/2)T^2 = 90
T = sqrt(180/g) = 4.29 s
V = 4/4.29 = 0.932 m/s

1. 👍
2. 👎
2. The problem is that you divided the distance traveled by the raft by ..4.49s.

I don't know where you got 4.49, but using the original time obtained by you with the time it takes for the rock to hit the water, would give you the answer in the book.

(time it takes for stone to hit water is same time traveled by raft)

1. 👍
2. 👎
3. thanks!

1. 👍
2. 👎
4. A woman on a bridge 75.0m high sees a raft floating at a constant speed on the river below. She drops a stone from rest in an attempt to hit the raft. The stone is released when the raft has 7.00m more to travel before passing under the bridge. The stone hits the water 4.00m in front of the raft. Find the speed of the raft.

1. 👍
2. 👎
5. How did you get the time,?

1. 👍
2. 👎

## Similar Questions

1. ### physics

70-kg man jumps off a raft 2 meter squared moored in a freshwater lake. By how much does the raft rise?

2. ### algebra

You live near a bridge that goes over a river. The underside of the bridge is an arch that can be modeled with the function y=-0.000475x^2+0.851x, where x and y are in feet. How high above the river is the bridge(the top of the

3. ### Physics

Here's the question: A 55 kg swimmer is standing on a stationary 235 kg floating raft. The swimmer then runs off the raft horizontally with a velocity of +4.3 m/s relative to the shore. Find the recoil velocity that the raft would

4. ### Physics

A rock dropped from a bridge takes 3.21 seconds to hit the water. How high is the bridge in meters? I need to find Vsub0 to be able to calculate h....but how do I get Vsub0???

1. ### Physics

A 60.0 kg girl stands up on a stationary floating raft and decides to go into shore. She dives off the 180 kg floating raft with a velocity of 4.0 m/s [W]. Ignore the substantial friction real objects in water experience. a) What

2. ### calculus

a bridge is 10 m. above a canal. A motorboat going 3 m/sec passes under the center of the bridge at the same instant that a woman walking 2 m/sec reaches that point. How rapidly are they separating 3 sec. later?

3. ### Pre calculus

The cable suspension bridge hangs in the shape of a parabola. The towers supporting the cable area is 600 lft apart and 200ft high. If the cable, at its lowest, is 40ft above the bridge at its midpoint, how high is the cable 50ft

4. ### physic

Bungee Jumping. A bungee jumper jumps from a tall bridge attached to a light elastic cord (bungee cord) of unstretched length L. The cord first straightens and then extends as the jumper falls. This prevents her from hitting the

1. ### Physics

A woman on a bridge 75.0m high sees a raft floating at a constant speed on the river below. She drops a stone from rest in an attempt to hit the raft. The stone is released when the raft has 7.00m more to travel before passing

2. ### physics help please!!!

A bungee jumper with mass 63.5 kg jumps from a high bridge. After reaching his lowest point, he oscillates up and down, hitting a low point eight more times in 40.0 s. He finally comes to rest 28.5 m below the level of the bridge.

3. ### Math, Trig

The high level bridge, a railway bridge that crosses the Oldman River is over 1km long. From one point on the river, the angle of elevation of the top of the bridge is 62.6 degrees. From a point 20m closer to the bridge, the angle

4. ### physical science

A bungee jumper jumps from a high bridge 100 m above a river. How fast does he fall after he has covered 60 m after jumping from the bridge? (Ignore air resistance in the fall.)