Simple Physics (unit analysis)

  • Thread starter Afide
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  • #1
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Homework Statement



1. (5 points)
If d is a distance, t is a time, and v is a speed, which of the following equations do unit analysis show must be wrong?

A. d = vt
B. v = 3 d^2 / t
C. t = d/v
D. v = d/t + 2 t/d
E. v = d^2 / t^2


I haven't done this since highschool and have no idea. It's pretty easy, but I don't remember this at all. Any help would be greatly appreciated, thanks guys!
 

Answers and Replies

  • #2
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Here's an effort of what I think its asking for..

A. d = vt
KM = KM/s(s) KM =/= KM^2 [WRONG]

B. v = 3 d^2 / t
KM/s^2 = 3KM^2 / sec KM/s^2 =/= km^2/s [WRONG]

C. t = d/v
sec = KM / KM/s^2 sec =/= s^2 [WRONG]

D. v = d/t + 2 t/d
KM/s^2 = KM/s + 2s/KM ???

E. v = d^2 / t^2
KM/s^2 = KM^2 / s^2 ???


idk.. >.<
 
  • #3
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Velocity is in m/s not m/s^2 or km if you want though meters is the standard.
 
  • #4
fss
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Here's an effort of what I think its asking for..
D. v = d/t + 2 t/d
KM/s^2 = KM/s + 2s/KM ???

E. v = d^2 / t^2
KM/s^2 = KM^2 / s^2 ???
In addition to distance usually being in meters (m) and the unit for velocity being distance/time (m/s) as Chunkysalsa pointed out,

For (D); do those two terms have the same units? If so, you're golden. If not, you have a problem.

For (E) you've done the dimensional analysis correctly, so ask yourself if the right hand side is in units of distance/time.
 

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