# Can you use momentum conservation to support your friend's case in court?

• Gregory
In summary, the conversation discusses a car accident and the need for support in court. The speed, momentum, and coefficient of kinetic friction between the cars and pavement are all mentioned. The conversation also includes attempts to solve the problem using various formulas and asking for help. In order to solve the problem, it is suggested to work backwards and compare the initial and final momentums. The conversation also includes a comment on the stereotypical gender roles in accidents.
Gregory
I have a problem, and I have no clue where to start- anyone have any help?

Your friend has been in a car accident and wants your help. She was driving her 1265-kg car north on Oak Street when she was hit by a 925-kg compact car going wast on Maple Street. The cars stuck together and slid 23.1m at 42° north of west. The speed limit on both streets is 50 mph (22 m/s). Your friend claims that she wasn't speeding, but that the other car was. Can you support her case in court? Assume that momentum was conserved during the collision and that acceleration was constant during the skid. The coefficient of kinetic friction between the tires and the pavement is 0.65.

Any help would be very appreciated... I am using the formula p=mv and p(A1)=P(1)sin x (The (A1) and (1) are subscripts)

I figured out that
Car 1 (Westward)
P(A) = (v*925kg)*(sin x) (again, (A) is a subscript of p)

Car 1 (Northward)
P(A) = (v*1265kg)*(cos x) (again, (A) is a subscript of p)

but, I'm not sure if that's even correct..

I was hoping F(f)=uF(N) would be useful, as its the only forumula I could find that uses the coefficient of friction (The (f) and (N) are subscripts, the "u" stands for the coefficient of friction- I couldn't find the right symbol for it)

I have a few diagrams drawn, but other than that, I couldn't figure out how to start...

Last edited:
Hmm...

How would I find the velocity? I was going to use KE=1/2 mv^2; but I can't figure out KE (I'm assuming that's what was being referred to by kinematics)...

I normally wouldn't ask for this much help, but after 2 hours of staring at forumlas with no result, I must admit I'm completely lost.

And, how does the kinetic coefficent come into play in this problem?

Thanks for your help- this is advanced for what I'm learning in school, so I don't have too much background knowledge to help me out..

Typically in problems, you are giving the initial conditions and you find the final. In this case, you are given the final conditions and are required to find the initial. So the best idea would be to work backwards. After the cars stuck together, what force was acting on them? Therefore, what acceleration was acting on them? If the final velocity is zero, then what must the initial velocity be? Then what must the momentum right after they hit each other (and before since it is conservered)? Compare this to your initial momentum.

Isn't it funny that, even in physics problems, it's the women who usually get into accidents?

## 1. What is momentum and how is it defined?

Momentum is a measure of an object's motion and is defined as the product of its mass and velocity. It is represented by the symbol "p" and has units of kg*m/s.

## 2. How is momentum conserved in a closed system?

Momentum is conserved in a closed system, meaning that the total momentum of all objects in the system remains constant. This is due to Newton's Third Law of Motion, which states that for every action, there is an equal and opposite reaction. Therefore, the total momentum before and after a collision or interaction must be the same.

## 3. Can momentum be transferred between objects?

Yes, momentum can be transferred between objects through collisions or interactions. In an elastic collision, both momentum and kinetic energy are conserved, while in an inelastic collision, only momentum is conserved. In both cases, the total momentum of the system remains constant.

## 4. How does mass and velocity affect an object's momentum?

The greater the mass and velocity of an object, the greater its momentum will be. This is because momentum is directly proportional to both mass and velocity, meaning that as these values increase, so does momentum.

## 5. Is momentum a vector or a scalar quantity?

Momentum is a vector quantity, meaning it has both magnitude and direction. The direction of an object's momentum is the same as its velocity, and the magnitude is equal to the product of its mass and speed.

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