- #1

eprparadox

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Thread moved from the technical forums, so no Homework Template is shown

Hey all, so I'm self studying and I came across this question:

A ## 2 kg ## cart, traveling on a horizontal air track with a speed of ## 3 m/s##, collides with a stationary ##4 kg## cart. The carts stick together. The impulse exerted by one cart on the other has a magnitude of:

A. ## 0 ##

B. ## 4 N \cdot s ##

C. ##6 N \cdot s ##

D. ## 9 N \cdot s ##

E.## 12 N \cdot s##

So I know the answer is B and that's fine. We find the final speed of the combined system as

[tex] v_f = \frac{ 2kg \cdot 3m/s}{2 kg + 4 kg} = 1 m/s [/tex]

The impulse is equal to teh change in momentum of the stationary cart and so that is just equal to [$] 4kg \cdot 1 m/s = 4 kg \cdot m/s [/$]. That's all good.

My question is more of how we know how long a force is exerted. For example, if the objects didn't stick together, then the force exerted would be over the time that the two objects were touching each other.

In this case, is there a way to know this? Is is just as soon as the acceleration stops and we're moving at the combined final speed which is found by conservation of momentum?

A ## 2 kg ## cart, traveling on a horizontal air track with a speed of ## 3 m/s##, collides with a stationary ##4 kg## cart. The carts stick together. The impulse exerted by one cart on the other has a magnitude of:

A. ## 0 ##

B. ## 4 N \cdot s ##

C. ##6 N \cdot s ##

D. ## 9 N \cdot s ##

E.## 12 N \cdot s##

So I know the answer is B and that's fine. We find the final speed of the combined system as

[tex] v_f = \frac{ 2kg \cdot 3m/s}{2 kg + 4 kg} = 1 m/s [/tex]

The impulse is equal to teh change in momentum of the stationary cart and so that is just equal to [$] 4kg \cdot 1 m/s = 4 kg \cdot m/s [/$]. That's all good.

My question is more of how we know how long a force is exerted. For example, if the objects didn't stick together, then the force exerted would be over the time that the two objects were touching each other.

In this case, is there a way to know this? Is is just as soon as the acceleration stops and we're moving at the combined final speed which is found by conservation of momentum?