# College Physics

posted by .

Two children are playing on a 178.2 m ­tall bridge. One child drops a rock (initial velocity zero) at t = 0 . The other waits 2.7 s and then throws a rock downward with an initial speed v0. If the two rocks hit the ground at the same time, what is v0 ?

for the first rock i used:
t(ground)=square root((2yo)/g)
... then I subtracted 2.7s from that number

I think you use Vo=(y-0)+.5gt^2/t

• College Physics -

I agree that the dropped rock takes sqrt(2Yo/g) = 6.03 s to teach the ground. The thrown rock must take 6.03 - 2.7 = 3.33 s from the timne it is thrown.

178.2 = Vo*t - (g/2)t^2

Solve for Vo.

Vo = (178.2 + 4.9 t^2)/t

With parentheses in the right place, and t = 3.33 s, you should get the right answer.

• College Physics -

does my answer need to be negative due to the rocks falling?

• High School -

-37.19 m/s

## Similar Questions

1. ### College Physics

Consider a rock thrown off a bridge of height 78.5 m at an angle è = 25° with respect to the horizontal as shown in Figure P4.20. The initial speed of the rock is 15.6 m/s. Find the following quantities: (a) the maximum height reached …

A ball is thrown downwards at a velocity of 14m/s from a bridge. One second earlier a rock is dropped from the same bridge. a)When will the ball meet up with the rock. b)When will the ball meet up with the rock?
3. ### Physics

Two children are playing on a 154-m-tall bridge. One child drops a rock (initial velocity zero) at t = 0. The other waits 1.1 s and then throws a rock downward with an initial speed v0. If the two rocks hit the ground at the same time, …
4. ### physics

A rock is dropped from a treetop 19.6 m high, and then, 1.00 s later, a second rock is thrown down. With what initial velocity must the second rock be thrown if it is to reach the ground at the same time as the first?
5. ### physics

A rock is dropped off of a bridge into the water below. If the initial velocity was zero, and the well is on Earth (g = 9.8 m/s2), and you see the splash 4.59 seconds after the rock was dropped, how high was the bridge above the water?
6. ### Physics

A hiker throws a rock with a mass of 1.4kg from a cliff that is 37 m above the ground . The hiker gives the rock an initial downward velocity of 8.5 m/s. a) What is the energy of the rock at the moment the hiker releases it?
7. ### Physics 270-1 Applied

A rock is thrown down with an initial speed of 30.0ft/s from a bridge to the water below. It takes 3.50s for the rock to hit the water. (a) Find the speed (in ft. /s) of the rock as it hits the water. (b) How high is the bridge above …
8. ### Physics

An attacker at the base of a castle wall 3.95 m high throws a rock straight up with speed 5.00 m/s from a height of 1.50 m above the ground. (a) Will the rock reach the top of the wall?
9. ### Physics

An attacker at the base of a castle wall 3.95 m high throws a rock straight up with speed 5.00 m/s from a height of 1.50 m above the ground. (a) Will the rock reach the top of the wall?
10. ### Physics

Two children are playing on a 147-m-tall bridge. One child drops a rock (initial velocity zero) at t = 0. The other waits 1.2 s and then throws a rock downward with an initial speed v0. If the two rocks hit the ground at the same time, …

More Similar Questions