Physics question involving velocity?

Question

Ugh. I stink at these types of questions. I simply cannot read graphs.

Please tell me how to use this graph

http://i299.photobucket.com/albums/mm320/waterpologoat/physics3.jpg

to find the instantaneous velocity at t=2.7s, t=4.2s, and t=7.3s.

You don't have to tell me the answers, just tell me how to figure it out, how to read the *@#$ graph!

lol.

Answer 1

Easy!

The horizontal line is the time (t).

So when it says t=2.7 s you just find the part on that line that is at 2.7.

Now look up to where the red line of the graph is right above the 2.7 s

Draw an imaginary line from that point all the way to the left. The number it hits is your answer. In this case 8

Answer 2

simple on the time line, go to 2.75, draw a line till u reach the graph, and check what the number on the y axis it is, like in t= 2.75,  x = 8 m

then u just use the formula V= x/t , substitute x and t, find v

V = x/t

   = 8/2.75

   = 2.909 m/s

repeat for every time given

at t = 4.2, x  = 5 ( i think it's five, not sure) but since it's a straight line, you instantly write down v = 0, because the object isnt moving,

at t = 7.3,  x = -4

substitute variables in formula, find v   :)

dont worry bout it being negative, it's supposed to ;)