Solving Vector Fnet: What is Fnet at Time t=0?

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At time t=0, the net force vector Fnet must point towards the center of the circular motion, which is the origin, indicating a direction of <4.5, 0, 0> m. The ball is in uniform circular motion, so the net force is centripetal, acting perpendicular to the velocity vector. Given one force F1 = < -261, 1764, 0 > N, the second force can be calculated using the equation Fnet = F1 + F2. The correct magnitude of the centripetal force was determined to be approximately 1306.67 N, confirming the direction of Fnet. Understanding the relationship between centripetal force and motion is crucial for solving such problems.
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In the dark in outer space, you observe a glowing ball of known mass 1.2 kg moving in the xy plane at constant speed in a circle of radius 4.5 m, with the center of the circle at the origin (< 0, 0, 0 > m). You can't see what's making it move in a circle. At time t=0 the ball is at location < -4.5, 0, 0 > m and has velocity < 0, 70, 0 > m/s.

a)
At time t=0, even though you can't see what's causing the motion, what can you conclude must be the direction of the vector Fnet?

b)You learn that at time t=0, two forces act on the ball, and that at this instant one of these forces is F1 = < -261, 1764, 0 > N. What is the other force?



Homework Equations


Fperpendicular is m(v^2/r)




The Attempt at a Solution


for the perpendicular force i got 1306.666667
which is right so i thought Fnet would be that or <0,1306.66667,0> but its not can someone please help? and idk how to do b please someone help!
 
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What is the direction of that net force? (Draw yourself a diagram of the motion.)
 
so would it be <0,j,0>?
and what about the 2nd questionnn?
 
ohheytai said:
so would it be <0,j,0>?
No.
and what about the 2nd questionnn?
First find the correct direction for Fnet, expressed as a vector. Then you can just use the vector equation Fnet = F1 + F2 to solve for the unknown force.
 
i don't get it how do you find the force then? it would be straight up would it be mass times velocity?
 
ohheytai said:
i don't get it how do you find the force then? it would be straight up would it be mass times velocity?
Did you draw a diagram of the motion, which is in the x-y plane?

You found the correct magnitude for the force, you just need the correct direction.
 
yes it would go straight up become Fnet is in the same direction of the momentum and velocity. so the direction would be <0,mv,0> right?
 
ohheytai said:
yes it would go straight up become Fnet is in the same direction of the momentum and velocity. so the direction would be <0,mv,0> right?
No. For uniform circular motion, what's the direction of Fnet?
 
Perpendicular? so it would be <mv,0,0>?
 
  • #10
ohheytai said:
Perpendicular? so it would be <mv,0,0>?
Momentum has nothing to do with it. Centripetal force always acts towards the center of the motion.
 
  • #11
okay so it is <mv,0,0> since the center is in the right?
 
  • #12
ohheytai said:
okay so it is <mv,0,0> since the center is in the right?
You have the correct direction, but 'mv' has nothing to do with it.
 
  • #13
ohhh wait wouldn't it be <Fperpendicular,0,0>?
 
  • #14
ohheytai said:
ohhh wait wouldn't it be <Fperpendicular,0,0>?
If by Fperpendicular you mean the centripetal force that you calculated, then yes.
 
  • #15
okay thanks you!
 
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