Height, time, gravity acceleration

[gigglin_horse]

Homework Statement

"A stone is thrown vertically upwards from the top of a building 29 metres high at an initial speed of 11 metres/sec. How long (in seconds) will it take the stone to hit the ground? The height at any time is given by

s = 29 + 11*t – 4.9*t2.

Give your answer correct to one rounded off decimal place (but don't round off as you work the problem), eg., 4.37 becomes 4.8."

Homework Equations

-29 = 11t - 4.9t^2
t(11 - 4.9t) = -29 <<< Do I do this? Do I need it?

The Attempt at a Solution

The answer is 3.801, but how do I get this?
Please help me

 

[LowlyPion]

Homework Statement

"A stone is thrown vertically upwards from the top of a building 29 metres high at an initial speed of 11 metres/sec. How long (in seconds) will it take the stone to hit the ground? The height at any time is given by

s = 29 + 11*t – 4.9*t2.

Give your answer correct to one rounded off decimal place (but don't round off as you work the problem), eg., 4.37 becomes 4.8."

Homework Equations

-29 = 11t - 4.9t^2

That's fine as far as it goes.

But what you have is a quadratic equation.

You can use the quadratic formula to solve the general equation:
http://en.wikipedia.org/wiki/Quadratic_equation#Quadratic_formula

One of the answers will give you your solution. The other root of the equation is likely a (-) number, indicating another solution of different construction that would also satisfy the same quadratic relationship.

 

[nlightner]

.

I would approach this problem by first identifying the given variables and equations. The problem provides the height of the building (29 meters), the initial speed of the stone (11 meters/second), and the equation s = 29 + 11t – 4.9t2 which relates the height of the stone to time.

Next, I would use the equation to solve for the time it takes for the stone to hit the ground. This can be done by setting s (height) equal to 0, since the stone will hit the ground when its height is 0. The equation then becomes 0 = 29 + 11t – 4.9t2.

To solve for t, we can use the quadratic formula or factor the equation to get t = 3.801 seconds. This is the time it takes for the stone to hit the ground.

In conclusion, as a scientist, I would solve this problem by using the given variables and equations and applying mathematical principles to find the solution. It is important to carefully analyze the problem and use appropriate equations to arrive at an accurate answer.