# [SOLVED] Mechanics Review Homework - Stuck =[

• Mar 12th 2009, 04:59 AM
Hammeh
[SOLVED] Mechanics Review Homework - Stuck =[
A body of mass 2kg is in equilibrium under the action of three coplanar forces, P, Q and R where P=3xi-2yj N, Q=2yi-4xj N, and R=-11i+4j N.

a) Calculate the values of x and y.
The force P ceases to act. Find.
b) The resulting acceleration of the body in component form.
c) The magnitude of the acceleration, giving your answer to 1 decimal place.

i and j are unit vectors.

I am completely confused by this question, can anyone offer up a method?
Thanks!
• Mar 12th 2009, 06:31 AM
skeeter
Quote:

Originally Posted by Hammeh
A body of mass 2kg is in equilibrium under the action of three coplanar forces, P, Q and R where P=3xi-2yj N, Q=2yi-4xj N, and R=-11i+4j N.

a) Calculate the values of x and y.
The force P ceases to act. Find.
b) The resulting acceleration of the body in component form.
c) The magnitude of the acceleration, giving your answer to 1 decimal place.

i and j are unit vectors.

I am completely confused by this question, can anyone offer up a method?
Thanks!

system is in equilibrium ... $\sum{F_i} = 0$ , $\sum{F_j} = 0$

3x + 2y - 11 = 0

-2y - 4x + 4 = 0

solve the system for x and y

P is taken away ... net force = Q + R

$a_i = \frac{F_i}{m}$ ... $a_j = \frac{F_j}{m}$

$
|a| = \sqrt{a_i^2 + a_j^2}
$

do it.
• Mar 12th 2009, 06:50 AM
e^(i*pi)
Quote:

Originally Posted by skeeter
system is in equilibrium ... $\sum{F_i} = 0$ , $\sum{F_j} = 0$

3x + 2y - 11 = 0

-2y - 4x + 4 = 0

solve the system for x and y

P is taken away ... net force = Q + R

$a_i = \frac{F_i}{m}$ ... $a_j = \frac{F_j}{m}$

$
|a| = \sqrt{a_i^2 + a_j^2}
$

do it.

And once you find a you can use pythagoras to find the magnitude
• Mar 12th 2009, 07:44 AM
skeeter
Quote:

Originally Posted by e^(i*pi)
And once you find a you can use pythagoras to find the magnitude

I thought I mentioned that ...

Quote:

$
|a| = \sqrt{a_i^2 + a_j^2}
$

• Mar 12th 2009, 08:02 AM
Hammeh
Thanks
Thanks skeeter, excellent method!