# Solving Momentum Questions: Intital vs Final Momentum

• rkslperez04
The mass of the cart is 150 kg. In summary, to find the mass of the cart in this problem, you can use the equation m1v1i + m2v2i = (m1 + m2)vf and solve for m2 by substituting the given values. The mass of the cart is found to be 150 kg.
rkslperez04
I need a nudge in the right direction.

A 50-kg boy runs at a speed of 10.0 m/s and jumps onto a cart originally at rest. The cart, with the boy on it, then takes off in them same direction in which the boy was running. If the cart with the boy has a veolocity of 2.50 m/s, what is the mass of the cart?

Would this me a Final Momentum = Intital Momentum problem?
How do I go about setting this up?

:)

rkslperez04 said:
I need a nudge in the right direction.

A 50-kg boy runs at a speed of 10.0 m/s and jumps onto a cart originally at rest. The cart, with the boy on it, then takes off in them same direction in which the boy was running. If the cart with the boy has a veolocity of 2.50 m/s, what is the mass of the cart?

Would this me a Final Momentum = Intital Momentum problem?
How do I go about setting this up?

:)

Hint: while calculating 'final momentum', the boy and the cart form a system.

ok... this is the formula I have

m1v1i + m2v2i = (m1 + m2)vf -----

I take it they are asking for the m2 and m2v2i willl cancel out being v2i = rest which is 0.

So do I pull everything to oneside and solve for m2

m2 = (m1 + m2)vf - m1v1i / v2i

I think I am doing something wrong

Last edited:
You set the equation up correct:

m1v1i + m2v2i = (m1 + m2)vf

The indices 1 are referring to the boy, and 2 to the wagon. As you said v2i equals zero, so you only have to solve for m2. So, $$m_{2} = \frac{m_{1}v_{1i}-m_{1}v_{f}}{v_{f}}$$.

ok.. I think i got it...Its soo funny.. I would never think of this during the winter... usually you just sled and go.. not caculate and go..LOL

I guess in a sled race.. this is all very important

(50)(10) - (50)(2.5) / 2.5 =

500 - 125 / 2.5 =

150 <~~ wieght of cart

rkslperez04 said:
150 <~~ wieght of cart

Yup, that's it.

## 1. What is momentum and why is it important to solve momentum questions?

Momentum is a measure of an object's motion and is calculated by multiplying its mass by its velocity. It is important to solve momentum questions because it helps us understand the movement of objects and how forces affect them.

## 2. What is the difference between initial and final momentum?

Initial momentum refers to the momentum of an object at the beginning of a given time period, while final momentum refers to the momentum of the same object at the end of the time period. The difference between these two values helps us understand the change in momentum of the object.

## 3. How do you calculate momentum?

Momentum is calculated by multiplying an object's mass (in kilograms) by its velocity (in meters per second). The formula for momentum is p = mv, where p is momentum, m is mass, and v is velocity.

## 4. What is the law of conservation of momentum?

The law of conservation of momentum states that the total momentum of a closed system (where no external forces are acting) remains constant. This means that the initial momentum of all objects in the system must equal the final momentum of all objects in the system.

## 5. How can you use the law of conservation of momentum to solve problems?

To solve problems using the law of conservation of momentum, you must first identify all objects in the system and their initial and final momentum values. Then, you can use the equation p(initial) = p(final) to solve for any unknown values. It is important to remember that the total momentum of the system must remain constant throughout the problem.

• Introductory Physics Homework Help
Replies
40
Views
3K
• Mechanics
Replies
15
Views
4K
• Mechanics
Replies
4
Views
16K
• Introductory Physics Homework Help
Replies
24
Views
2K
• Introductory Physics Homework Help
Replies
4
Views
1K
• Introductory Physics Homework Help
Replies
10
Views
928
• Classical Physics
Replies
3
Views
457
• Introductory Physics Homework Help
Replies
5
Views
6K
• Introductory Physics Homework Help
Replies
1
Views
3K
• Introductory Physics Homework Help
Replies
19
Views
1K