Kinematics - What do these variables mean?

  • Thread starter kbn
  • Start date
  • #1
kbn
2
0

Homework Statement


first off, i dont completely understand what do the variables in the equation do:

x=Xo+Vot+1/2at2

the exercise:
A body is thrown up vertically, it passes trough the height 9,8m twice. Time between those two passes is 4 seconds. Whats the starting velocity ?


Homework Equations





The Attempt at a Solution



i presume i have to do it with two equation systems? first off i'd have to calculate the starting velocity needed to get up and down in four seconds. Then i'd calculate the starting speed needed to get to the "seconds starting speed" at 9,8m and that would be the answer.

Bigthnx
 

Answers and Replies

  • #2
mjsd
Homework Helper
726
3
[tex]x=x_0 + v_0 t + \frac{1}{2} a t^2[/tex]
[tex]x[/tex] is displacement at time [tex]t[/tex]
[tex]x_0[/tex] is initial displacement
[tex]v_0[/tex] is initial velocity
[tex]a[/tex] is acceleration (constant)
[tex]t[/tex] is time

hint: [tex]a=9.8 m/s^2[/tex] in this case
 
  • #3
mjsd
Homework Helper
726
3
oh.. new to PF.. welcome :smile:
 
  • #4
kbn
2
0
great thanks for explaining the equation for me (y) everything seems much clearer now.

So i tried to solve it, but the answer isnt what its supposed to be =/ I mean, it different in the end of the book. Is the book wrong or am i ?

9,8=0 + Vo4 - 1/2*9,8*4[tex]^{2}[/tex]

4Vo = 1/2*9,8*4[tex]^{2}[/tex] + 9,8

Vo= (1/2*9,8*4[tex]^{2}[/tex] + 9,8) / 4 = 22,05 m/s

According to the textbook the answer should be 24 m/s

Thanks again
 

Related Threads on Kinematics - What do these variables mean?

  • Last Post
Replies
7
Views
1K
  • Last Post
Replies
10
Views
2K
  • Last Post
Replies
3
Views
1K
Replies
8
Views
963
  • Last Post
Replies
3
Views
1K
Replies
1
Views
4K
  • Last Post
Replies
4
Views
2K
Replies
3
Views
2K
Replies
7
Views
4K
Top