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Particle moving in a circle - MULTIPLE CHOICE! Please help.

For a particle moving in a circle with uniform speed, which one of the following statements is correct?

A: The kinetic energy of the particle is constant

B: The force on the particle is in the same direction as the direction of motion of the particle

C: The momentum of the particle is constant.

D: The displacement of the particle is in the direction of the force.

Apparently the answer is A... but Ke = 1/2 M V^2
and momentum = MV .. they both contain MV so if ke is constant, momentum must be constant???? so why isn't C correct? PLEASE Explain...
(edited 9 years ago)
Original post by Jordan Jones
For a particle moving in a circle with uniform speed, which one of the following statements is correct?

A: The kinetic energy of the particle is constant

B: The force on the particle is in the same direction as the direction of motion of the particle

C: The momentum of the particle is constant.

D: The displacement of the particle is in the direction of the force.

Apparently the answer is A... but Ke = 1/2 M V^2
and momentum = MV .. they both contain MV so if ke is constant, momentum must be constant???? so why isn't C correct? PLEASE Explain...


Momentum is a vector quantity; it has a magnitude AND a direction. As the direction of the particle is continually changing in the circle, the momentum can't be constant.
Reply 2
Avatar for Jordan Jones
Jordan Jones
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Original post by usycool1
Momentum is a vector quantity; it has a magnitude AND a direction. As the direction of the particle is continually changing in the circle, the momentum can't be constant.


isn't velocity a vector quantity with a magnitude and direction also? So if the direction is constantly changing, how is KE constant if it contains velocity?
(edited 9 years ago)
Original post by Jordan Jones
isn't velocity a vector quantity with a magnitude and direction also? So if the direction is constantly changing, how is KE constant if it contains velocity?


In the KE equation, velocity is squared, so as when 2 squared and -2 squared both equal 4, just the magnitude, the same thing happens here, so velocity squared is just a magnitude
Reply 4
Avatar for Jordan Jones
Jordan Jones
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Original post by Sam280297
In the KE equation, velocity is squared, so as when 2 squared and -2 squared both equal 4, just the magnitude, the same thing happens here, so velocity squared is just a magnitude


ahh ok.. thanks alot.
Original post by Jordan Jones
x


You have the right approach: as you surely know, the kinetic energy is depend on mass and velocity (=speed). Say, the mass of the particle is in every single point of the circle the same, the speed as written above too. So the kinetic Energy must be the same in a moving circle.
(edited 9 years ago)

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