Question

A child drops his toy car from a 2nd floor window that is 7.3 meters high. Find the velocity of the toy car just before it hits the ground below. Ignore any affects of air resistance.

**not sure how to do this one! :/ thank you:)

Answer 1

I would write down the formulas you know... (I do that to waste time until a good thought happens...)

Answer 2

haha okie!
so f=m*a
v(t)=v0+a*t
v(t)=a*t
ermm not sure what other ones would apply here?

Answer 3

the distance = 1/2 a t^2

Answer 4

ohh so is that what i use for this problem?

Answer 5

also a= g = 9.8 m/s or 32 ft/sec

Answer 6

next, write down the numbers (variables that have know values)
which equations (if any) can be solved for an unknown variable?
if we do solve, will that be helpful ?

Answer 7

so 7.3=height?

and final velocity would be 0 ?

Answer 8

@phi?

Answer 9

do you know the Torricelli formula? @iheartfood

Answer 10

yes, but i forget which equation that is:/

Answer 11

7.3 m = 1/2 9.8 m/s^2 t^2
solve for t

Answer 12

after you find t, use v= 9.8 t to find the velocity.

Answer 13

oh, so 7.3=4.9 * t^2
2.4=t^2 ?
t=1.55?

@phi?

Answer 14

7.3=4.9 * t^2
t^2= 7.3/4.9 = ?

Answer 15

t^2= 1.489 = 1.49 ?

Answer 16

t=1.22 ? @phi?

Answer 17

yes, that looks better.
now you can find v , right ?

Answer 18

is it v=a*t ?

Answer 19

v= 9.8 and t=1.22 ? solve for a? or is something else? :/

Answer 20

a is acceleration (here due to gravity) and we know a. (it's "g" =9.8 m/s^2 )
we don't (yet) know v after falling for 1.22 seconds

Answer 21

ohh okay!

so v=9.8 * 1.22
v=11.956 m/s ?

Answer 22

but put in the units

Answer 23

oh like v= 9.8 m/s^2 * 1.22 s = 11.956 m/s ?

Answer 24

\[ v=9.8 \frac{m}{s^\cancel2} 1.22 \cancel{s} = 11.956 \frac{m}{s}\]
after we "cancel" the seconds, the final units work out to m/s. This shows we are probably correct.. we got the expected units.

Answer 25

ah yes!! :) yay thank you so much @phi :)

Answer 26

yw