# Thread: Intergration and Vertical Motion

1. ## Intergration and Vertical Motion

Hi, I'd appreciate any help on this!

1. With that velocity must an object be thrown upward from ground level to reach a max. height of 200 m?

2. The acceleration due to gravity is -1.6 m/s on the moon. If a stone is dropped from a cliff and hits the surface 20 seconds later, what was its velocity at impact?

Thanks!

Hi, I'd appreciate any help on this!

1. With that velocity must an object be thrown upward from ground level to reach a max. height of 200 m?

2. The acceleration due to gravity is -1.6 m/s on the moon. If a stone is dropped from a cliff and hits the surface 20 seconds later, what was its velocity at impact?

Thanks!
1)

max height$\displaystyle =s=200$
$\displaystyle a=g=-10$
$\displaystyle v=0$
$\displaystyle u=?$

$\displaystyle v^2=u^2+2as$
$\displaystyle 0=u^2+2(-10)(200)$
$\displaystyle u=20(10)^{\frac {1}{2}}$

2)

$\displaystyle a=g=+1.6$(drop, therefore positive)
$\displaystyle t=20$
$\displaystyle u=0$
$\displaystyle v=?$

$\displaystyle v=u+at$
$\displaystyle v=(0)+(+1.6)(20)$
$\displaystyle v=32$ (positive just the direction)

3. I just want to mention here that $\displaystyle g = 9.8~m/s^2$, not 10.

-Dan

4. Originally Posted by topsquark
I just want to mention here that $\displaystyle g = 9.8~m/s^2$, not 10.

-Dan

I know that, but I only a Form 5 student just after SPM(same standard as "O" level). In SPM, $\displaystyle g=10m/s^2$ when doing calculation.

5. Originally Posted by SengNee
I know that, but I only a Form 5 student just after SPM(same standard as "O" level). In SPM, $\displaystyle g=10m/s^2$ when doing calculation.
What? Gravity changes depending on what level class you are in!?

6. Originally Posted by TKHunny
What? Gravity changes depending on what level class you are in!?
I not mean that.
Front pages of SPM Physics Paper list formula and constant for us.
g=9.8≈10
In the Physics Paper, the constant g listed as g=10 and our calculation also use g=10 to make our calculation easier.

I'm sorry about that, I will use g=9.8 next times.

7. Maylasia is not alone in using this bewildering approximation: In Australia (or Victoria at least), acceleration due to gravity is 10m/s^2 until you reach university level.

Maylasia is not alone in using this bewildering approximation: In Australia (or Victoria at least), acceleration due to gravity is 10m/s^2 until you reach university level.
I've heard of a couple of US High Schools that do this too. Apparently it is an effort to make the numbers "easier" for the students.

-Dan

Maylasia is not alone in using this bewildering approximation: In Australia (or Victoria at least), acceleration due to gravity is 10m/s^2 until you reach university level.
So, why they keep on said that g must equal to 9.8.

10. Originally Posted by SengNee
So, why they keep on said that g must equal to 9.8.
Because that is a lot closer to the measured value? I'm not sure what you mean?

For the record I am against making the numbers easier on the students. There was a survey done (sometime in the mid 80s?) where students who had done all their schoolwork in problems where the numbers always canceled out nicely etc, etc. This was fine until they got to the real world and the numbers got ugly. The problem was that they had no confidence in their answers if it didn't come out to be a nice integer.

For the Applied Sciences anyway, I say that decimal numbers rule!

-Dan

11. Originally Posted by topsquark
I've heard of a couple of US High Schools that do this too. Apparently it is an effort to make the numbers "easier" for the students.

-Dan
It's very very ridiculous.

In this day and age of ubiquitous technology, that you would prescribe g = 10 rather than 9.8 in "an effort to make the numbers "easier" for the students" is diabolical.

Some of the folk sitting on these curriculum panels need to have a good hard look at themselves ....

12. Originally Posted by topsquark
Because that is a lot closer to the measured value? I'm not sure what you mean?

For the record I am against making the numbers easier on the students. There was a survey done (sometime in the mid 80s?) where students who had done all their schoolwork in problems where the numbers always canceled out nicely etc, etc. This was fine until they got to the real world and the numbers got ugly. The problem was that they had no confidence in their answers if it didn't come out to be a nice integer.

For the Applied Sciences anyway, I say that decimal numbers rule!

-Dan
Hear hear.

I am in complete agreement with you.