If an object was dropped from a building 80m above the ground, how long would it take for it to hit the ground?
Please help, I'm stuck...
+118724 
s=80 a=9.8 u=0 t= ??
None of those fromulas have got just s a u and t so maybe we will use 2 formulas
No 4
$$\\v^2=u^2+2as\\
v^2=0+2*9.8*80\\
v^2=1568\\
v=39.6m/s$$
Now I will use no1
$$\\v=u+at\\
39.6=0+9.8*t\\
t=39.6/9.8\\
t=4.04 seconds$$
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You can also use calculus to solve this.
$$\\ \ddot{y} = -9.8\\
\dot{y}=-9.8t\\
y=-9.8/2*t^2+80\\
y=-4.9t^2+80\\
when y=0
0=-4.9t^2+80\\
4.9t^2=80\\
t^2=80/4.9\\
t=4.04 seconds$$
+118724
s=80 a=9.8 u=0 t= ??
None of those fromulas have got just s a u and t so maybe we will use 2 formulas
No 4
$$\\v^2=u^2+2as\\
v^2=0+2*9.8*80\\
v^2=1568\\
v=39.6m/s$$
Now I will use no1
$$\\v=u+at\\
39.6=0+9.8*t\\
t=39.6/9.8\\
t=4.04 seconds$$
---------------------------------------
You can also use calculus to solve this.
$$\\ \ddot{y} = -9.8\\
\dot{y}=-9.8t\\
y=-9.8/2*t^2+80\\
y=-4.9t^2+80\\
when y=0
0=-4.9t^2+80\\
4.9t^2=80\\
t^2=80/4.9\\
t=4.04 seconds$$
