question wrote:

It's height is h after t1 and t2 seconds

Just one h for both times. Once on the way up and then again on the way down.

Bob

]]>hi markosheehan

Use

a = -g, Write the two equations for h with t1 and t2. Equate to get an expression for u in terms of g, t1 and t2. Substitute back into either to eliminate u.

Bob

ps. Why did I do it this way? The problem involves height, gravity, initial velocity and time so that forces which equation to use. With two equations you can eliminate one variable. I chose h because it looked easiest but then had to rework to eliminate u. Maybe I should have made u the subject of the two and equated those to get the answer straight off. I leave it to the reader to try that if desired.

pps. Tried it myself and it comes out easily this way in four lines.

Hi,

I followed that, but we still have then h1 (at t1) and h2 (at t2)..

[t1.h2-t2.h1]/t1.t2=0.5g[t1-t2]

what do you think ?

]]>final t is comprised of t1 of t2 times .. in other words -> t_final=t1*t2 (considering that t2 is just a unit less number)

-- Applying motion equation:

v= u-gt // minus because its going up

but v when particle reaches the top = 0

0=u-gt

u=gt..

lets integrate this over time..

h=0.5gt^2

//substitute: t=t1*t2

h=0.5g[t1*t2]^2

//arranging the equation..

[t1*t2]^2 = 2h/g // but i know its not correct since units are not compatible on both sides-> unless considering the whole set of t1*t2 is of second's unit but not second square, as pre my assumption t=t1*t2 !

then i can say:

t1*t2 = 2h/g]]>

Use

a = -g, Write the two equations for h with t1 and t2. Equate to get an expression for u in terms of g, t1 and t2. Substitute back into either to eliminate u.

Bob

ps. Why did I do it this way? The problem involves height, gravity, initial velocity and time so that forces which equation to use. With two equations you can eliminate one variable. I chose h because it looked easiest but then had to rework to eliminate u. Maybe I should have made u the subject of the two and equated those to get the answer straight off. I leave it to the reader to try that if desired.

pps. Tried it myself and it comes out easily this way in four lines.

]]>