Physics Question

[Sarahisme]

Hey just wanted to check my answer for this question

damn answers in back of book only being for every 2nd question

 

i get v = 1.40m/s

 

well heres the question

[swansont]

Show your work!

[Sarahisme]

you mean working?

[Dave]

Indeed. We can't really check otherwise

[Sarahisme]

ok sure, i will just write it up now

[Sarahisme]

ok here is what i did.....

(dEmech, means delta Emech, and so on)

Wext = dEmech = 0 = dKE + dPE

 

define PE=0 where the 2kg is initially.

therefore PEi = m1gh + m2gh

= m1g

 

KEi = 0

 

m1g = PEf + KEf

= m1gh + m2gh + .5m1v1^2 + 0.5m2v2^2

= gh(m1 + m2) + .5v^2(m1+m2)

m1g = (m1 + m2)(gh + .5v^2)

v^2 = 2(m1g/(m1+m2)-gh)

subing in values for m1, m2, g and h.

h is 0.5 because of the length of the rope attaching the two blocks. (the only possible height when they can be at the same height is when h = 0.5m)

 

so therefore

v = 1.40m/s or 1m/s (because the quesiton only has one sig figure)

[swansont]

Looks good to me!

 

The reason for asking to show your work is that there are some ways to do a problem incorrectly (like making two mistakes that cancel in the math) that still give the right answer.

[Sarahisme]

oh ok, yeah i know what ya mean

 

well thanks for that then