# Calculating Impulse Without Force or Time

• Skye425
In summary, the conversation discusses a physics homework problem involving two objects colliding. The initial momentum and masses of the objects are given, but the forces and time are not specified. The question asks for the impulse applied to the system by external forces, but without more information, it is impossible to calculate. The conversation concludes by suggesting that there may be no external force or impulse at all.
Skye425

"Object A has mass mA = 7 kg and initial momentum vector pA,i = < 17, -8, 0 > kg · m/s, just before it strikes object B, which has mass mB = 11 kg. Just before the collision object B has initial momentum vector pB,i = < 3, 5, 0 > kg · m/s.
The forces that A and B exert on each other are very large but last for a very short time. If we choose a time interval from just before to just after the collision, what is the approximate value of the impulse applied to the two-object system due to forces exerted on the system by objects outside the system?"

i already calculated the total momentum of the system to be <20, -3, 0> kg m/s but i just can't figure out how to calculate the impulse without a given force or time.

Last edited:
There is no way to tell from the information given. Are you sure you stated the problem correctly?

First of all, there's no time, so impulse cannot be found.

Also, you cannot analyze a collision of any sort withou knowledge of what kind of collision it is. Therefore the total momentum of the system is a useless value, because you don't know if the collision is elastic, inelastic, or something in between.

Finally, it asks for the force exerted by an external force, but it isn't stated what happens to the system. If the time is immediately after the collision, there is no external force on the system at all yet.

Actually, that might be the answer. No force or impulse at all from the outside.

## 1. How do you calculate impulse without force or time?

To calculate impulse without force or time, you can use the equation impulse = mass x change in velocity. This equation is based on Newton's second law, which states that force equals mass times acceleration. By rearranging the equation, you can solve for impulse without needing to know the force or time.

## 2. Can you give an example of calculating impulse without force or time?

Yes, for example, if a 2 kg object is moving at a velocity of 5 m/s and then changes its velocity to 10 m/s, the change in velocity would be 5 m/s. To calculate the impulse, you would multiply the mass (2 kg) by the change in velocity (5 m/s), resulting in an impulse of 10 kg*m/s.

## 3. Why is it useful to calculate impulse without force or time?

Calculating impulse without force or time can be useful in situations where the force or time is unknown or difficult to measure. It allows you to still determine the change in momentum of an object, which is important in understanding the overall motion and interactions of objects.

## 4. What units are used for impulse?

The units for impulse are usually expressed as kg*m/s, which can also be written as Newton seconds (N*s). This is because impulse is a combination of mass and velocity, which are measured in kilograms and meters per second, respectively.

## 5. Can you calculate impulse without knowing the initial and final velocities?

No, knowing the change in velocity is necessary to calculate impulse without force or time. If only one velocity is known, it is not possible to determine the change in velocity and therefore the impulse. However, if the initial and final velocities are the same, the change in velocity would be 0 and the impulse would also be 0.

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