# The momentum of a car moving at a constant…

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## The momentum of a car moving at a constant speed in a circular track

• A. Can be both positive and negative
• B. Can be centripetal
• C. Can be zero depending on its position in the track
• D. Can be centrifugal

A

## DETAILS…

Be careful with this question, your understanding of the basic difference between a vector quantity (like velocity) and a scalar quantity (like speed) will make the difference.

A body may be travelling with constant speed in a circle, but this does not imply that the velocity is also constant. This is because velocity is a vector which in addition to magnitude, also depends on direction.

Now, as the body moves with constant speed IN A CIRCLE, its velocity will not be constant, but will be changing as the direction of the body changes.

However, because momentum is simply another vector which can be calculated as = mass X change in velocity, the only condition for a zero momentum is if the velocity is constant, but fortunately we have a changing velocity.

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Hence, the momentum for a body travelling in a circle can never be zero but may be negative or positive depending on the current direction of the body.

### Now for the right answer to the above question:

1. Option A is correct. depending on the direction, a body moving in a circle will have either positive or negative momentum.
2. Option B is incorrect. cannot be centripetal because the direction of movement is not away from the center but along the circumference of the circle.
3. C is incorrect. can NEVER be zero as long as it moves in a circular path.
4. D is not the correct answer. cannot be centrifugal because the direction of movement is not towards the center but along the circumference of the circle