Posted by **Megan** on Friday, May 25, 2012 at 2:42pm.

Sam tosses a ball horizontally off a footbridge at 4.3 m/s. How much time passes after he releases it until its speed doubles?

Can someone please explain the correct equation to use thoroughly and help me to find the correct answer?!

- Physics -
**Steve**, Friday, May 25, 2012 at 2:52pm
by speed, do you mean the vector sum of the horizontal and vertical speeds?

Must be, since the horizontal speed never changes, and the initial vertical speed was 0, so double that is still 0.

**v** = 4.3**i** - 9.8t**j**

|**v**| = √(4.3^2 + (9.8t)^2) = √(96.04t^2 + 18.49)

so, double the original speed is 8.6m/s and we want to find t when

8.6 = √(96.04t^2 + 18.49)

t = 0.76 sec

- Physics -
**Elena**, Friday, May 25, 2012 at 2:54pm
This is the projectile thrown with horizontal velocity.

So

v(x) = const,

v(y) = g•t.

v ² = v(x)² +v(y)²

v =2•v(x),

[2v(v)]² = v(x)² +v(y)²,

3•v(x)² =v(y)² = (g•t)²,

t =v(x) •√3/g =4.3•1.73/9.8 =0.76 s.

## Answer this Question

## Related Questions

- physics - Sam tosses a ball horizontally off a footbridge at 4.8 m/s. How much ...
- physics - Sam tosses a ball horizontally off a footbridge at 3.1 m/s. How much ...
- physics - Sam tosses a ball horizontally off a footbridge at 3.2 m/s. How much ...
- physics - umm i need help...which equation would i use to solve the probnlem ...
- physics - i posted this question before however i did not understand drwls ...
- physics - A boy reaches out of a window and tosses a ball straight up with a ...
- Physics/Science #3 - A ball is thrown vertically downward from the top of a 35.9...
- Physics - At the beginning of a basketball game, a referee tosses the ball ...
- Physics - An eagle is flying horizontally at 5.8 m/s with a fish in its claws. ...
- Physics - An eagle is flying horizontally at 7.9 m/s with a fish in its claws. ...