physics question

[2010premed]

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If the acceleration is 20m/s^2 to the right, and the object travels for 4 seconds, what is the distance?

Can I do it this way?

first second: v = 20m/s d = 20m
second second: v = 40 m/s total d = 60m (40 + 20)
third second: v= 60m/s total d = 120m (60+40+20)
fourth second: v=80m/s total d = 200m (80+60+40+20)

Howcome I get a different answer if I plug into x = v0t + 1/2at^2?
if v0t = 0, the x = 160m

 

[fizzgig]

you can do it your way, but during each second you need to use the AVERAGE velocity during that second.

avg Vels are 10,30,50,70, 1 s each, =160

 

[2010premed]

ahh, k thanks