- #1

- 16

- 0

1.05 = (ViSin30)10 * ViCos30+ 1/2(-9.8)(10/ViCos30)^2

help me solve for Vi please

help me solve for Vi please

- Thread starter bmore007
- Start date

- #1

- 16

- 0

1.05 = (ViSin30)10 * ViCos30+ 1/2(-9.8)(10/ViCos30)^2

help me solve for Vi please

help me solve for Vi please

- #2

- 5,753

- 1,050

You might want to take care in using parenthesis around (ViCos30), especially in the second term on the right-hand side.

- #3

- 16

- 0

all the #'s i'm getting are turning out wrong

- #4

- 5,753

- 1,050

Can you factor "(ViSin30)10 * ViCos30" ?

It may help to forget the numbers and think of this symbolically as [tex](V_i A)B * V_iC[/tex]. So, can you factor this expression and write it in terms of [tex]V_i[/tex], [tex]A[/tex], [tex]B[/tex], and [tex]C[/tex]?

- #5

- 16

- 0

"Can you factor "(ViSin30)10 * ViCos30" ?"

4.33Vi

4.33Vi

- #6

- 5,753

- 1,050

almost... correct coefficient...

check the units of that term

check the units of that term

- #7

- 16

- 0

i dont understand why that isnt correct

ViSin(30)*10 * ViCos(30)

Vi.5 * 10 * Vi .87

Vi 4.4

ViSin(30)*10 * ViCos(30)

Vi.5 * 10 * Vi .87

Vi 4.4

- #8

- 5,753

- 1,050

that term should have a Vi^2

- #9

- 16

- 0

- #10

- 5,753

- 1,050

ViSin(30)*10 * ViCos(30) = Vi^2 4.4

You've done fine with the coefficient, although you missed the fact that Vi is squared.

But you've gotten passed that. In other words, algebra (rather than arithmetic) is your problem.

Now, work on factoring "1/2(-9.8)(10/ViCos30)^2", which you should really write as (1/2)(-9.8)(10/ (ViCos30) )^2... especially if you try to plug something like this into your calculator.

- #11

- 16

- 0

unfortunately i'm not too good at more involved algebra like this

(1/2)(-9.8)(10/ (ViCos30) )^2

-4.9(100/Vi^2* .75)

so

4.4Vi^2 -4.9(100/.75Vi^2)

(1/2)(-9.8)(10/ (ViCos30) )^2

-4.9(100/Vi^2* .75)

so

4.4Vi^2 -4.9(100/.75Vi^2)

Last edited:

- #12

Integral

Staff Emeritus

Science Advisor

Gold Member

- 7,201

- 56

Is this the starting point:

[tex] 1.05 = V_i Sin(30) * 10 * V_i Cos(30) + \frac {-9.8} {2} \frac {10} {{(V_i Cos(30))}^2}[/tex]

- #13

- 16

- 0

yes that is the starting point

except it's (10/ViCos30)^2

the whole thing squared

except it's (10/ViCos30)^2

the whole thing squared

- #14

- 16

- 0

n/m

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