# Physics

Discussion in 'Electronics Homework Help' started by Integrator741, Mar 15, 2016.

1. ### Integrator741

125
4
Jun 16, 2013
Good Evening Everyone,

I think I have it right - just don't have an example to double check.

"An Object is projected vertically upwards from ground level at 49 m s^-1. Find its height after 1 s, 3 s, 5 s, 7 s, 9 s. What is its total time of flight?"

I've answered the first part of this question using "s = ut+1/2at^2" and it seems that I got that right.
Now, "when they say what is its total time of flight" do they mean both ways? Because the answer is 10s, but using "v=u+at" I get 5s. So if it is both ways then I am right, if not, I must have done something wrong.

Thank you.

2. ### Gryd3

4,098
875
Jun 25, 2014
There is no additional details regarding how it's landing. I'm sure it would be safe to assume total flight if it was shot vertically would be the time it takes to return to it's initial starting point.

3. ### davennModerator

13,654
1,888
Sep 5, 2009
and don't forget the effects of gravity acting on the object
unless the problem specifically stated to ignore it

4. ### dorke

2,342
665
Jun 20, 2015
You did fine.
Vi=initial speed
g=-9.8m/s^2 (gravity)

V(t)=Vi+g*t
at the top of the trajectory V(t)=0 ,thus
0=Vi+g*t ,so
t=-Vi/(-g) = Vi/9.8
t(TOP)=49 /9.8=5sec (time to the top)

The total time of flight is
T(Tot)= 2*t(TOP)=10sec

Integrator741 and hevans1944 like this.
5. ### Integrator741

125
4
Jun 16, 2013
Thank you.  