An object is thrown upwards and after 2 seconds is 78 m above where it was initially thrown. Assume no air resistance, and determine the initial speed the object was thrown at.

Question

An object is thrown upwards and after 2 seconds is 78 m above where it was initially thrown.  Assume no air resistance, and determine the initial speed the object was thrown at.

istim · Answer

Wrong group.

amistre64 · Answer

right group ... kinda

istim · Answer

Sorta. Physics.

amistre64 · Answer

we are in meters so -4.9

assume 0 for initial height

rogue · Answer

$$s(t) = - \frac {1}{2} g t^2  + v_0 t + s_0$$

amistre64 · Answer

-4.6 t^2 + V t = 78

amistre64 · Answer

6, 9, not much difference eh

istim · Answer

Just use the Kinematics equations, right?

anonymous · Answer

what does 78m stand for?
displacement, distance, or velocity?

amistre64 · Answer

kinetics are for babies and old ladies ....

istim · Answer

Kinematics aren't kinetics. But okay.

istim · Answer

78m has no direction, and also speed is m/s.

anonymous · Answer

but it says upwards :s

istim · Answer

If it says upwards, then its displacement.

amistre64 · Answer

|dw:1329871307054:dw|

it might be easier to assume its a vertex

amistre64 · Answer

a minimum velocity perhaps :)

anonymous · Answer

kk. thanks what is -4.9? how did we get that?

amistre64 · Answer

-4.9(4) + V(2) - 78 = 0

V = 39 +4.9(2)

maybe

-4.9 is gravity holding us back

amistre64 · Answer

since we are in meters

istim · Answer

Wait. I'm stupid. Isn't gravity 9.8?

anonymous · Answer

yeah gravity is 9.8.

amistre64 · Answer

acc due to g is 9.8

velocity = 9.8t

position = 9.8t^2/2 = 4.9 t^2

but since gravity is a downward force; -4.9 t^2

istim · Answer

Makes sense.

istim · Answer

With that explained, I think we are done.

amistre64 · Answer

but .... im too old to die!!

istim · Answer

"You're never to young to die"-A quote that makes me sad.