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Old Nov 18th 2008, 05:19 PM   #1
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Velocity vs time graph and questions

Question Details:
The graph shows the change in the velocity of an object with time in a situation in which momentum is conserved. which of the following situations is most likely indicated by the graph. explain why or why not the situations is or is not the best choice..



Hint: think about conservation of linear momentum and conservation of energy to solve the problem.



A) The velocity of a bullet striking a ballistic pendulum

B) The velocity of a car colliding head on with another car of equal weight and velocity

C) The velocity of a fixed stationary object being hit by a bullet

D) The velocity of a swinging pendulum

E) A ball rolling across a level floor
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Old Nov 18th 2008, 05:35 PM   #2
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id say choice d
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Old Nov 18th 2008, 06:06 PM   #3
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No, it's not d) because in that case the velocity changes of sign each half period. Also its velocity is never constant.

I'd say A) because the velocity of the bullet would remain constant until hitting the ballistic pendulum. When it hits it the velocity would go down but not equal to $\displaystyle \frac{0m}{s}$ (as shown in the graph) because it would encrust into the pendulum and follow it's path at a lower speed according to the conservation of linear momentum.

However I dislike the graph because he hasn't any scale-time reference so we must find out if the time is short (less than $\displaystyle 1 s$) or long (more than $\displaystyle 1s$).

It's not B) because the car would remain quiet after the collision (means that velocity is worth $\displaystyle \frac{0m}{s}$).

Nor C) because its velocity would increase (starting from $\displaystyle \frac{0m}{s}$).
And I don't know about the E) because I don't know what a level floor is.
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