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Object A is moving due east, while object B is moving due north. They collide and stick together in a completely inelastic collision. Momentum is conserved. Object A has a mass of \(m_{A}=17.0 \mathrm{kg}\) and an initial velocity of \(\overrightarrow{\mathbf{v}}_{a \Lambda}=8.00 \mathrm{m} / \mathrm{s},\) due east. Object \(\mathrm{B},\) however, has a mass of \(m_{\mathrm{B}}=29.0 \mathrm{kg}\) and an initial velocity of \(\overrightarrow{\mathrm{v}}_{\mathrm{oB}}=5.00 \mathrm{m} / \mathrm{s},\) due north. Find the magnitude and direction of the total momentum of the two- object system after the collision.

Short Answer

Expert verified
Magnitude: 198.8 kg·m/s; Direction: 46.7° from east towards north.

Step by step solution

01

Determine the initial momentum of Object A

The momentum of an object is calculated by multiplying its mass by its velocity. For Object A, the initial momentum is \( p_{A} = m_A \times v_{a} = 17.0 \, \text{kg} \times 8.00 \, \text{m/s} = 136.0 \, \text{kg} \cdot \text{m/s} \) due east.
02

Determine the initial momentum of Object B

Similarly, the initial momentum of Object B is \( p_{B} = m_B \times v_{b} = 29.0 \, \text{kg} \times 5.00 \, \text{m/s} = 145.0 \, \text{kg} \cdot \text{m/s} \) due north.
03

Calculate the total momentum after the collision

Since momentum is conserved, the total momentum before the collision equals the total momentum after the collision. This total momentum can be represented as a vector sum of the momenta of Objects A and B: \( \vec{p}_{\text{total}} = \vec{p}_{A} + \vec{p}_{B} \).
04

Find the magnitude of the total momentum

The magnitudes of the momenta vectors form a right triangle, as Object A's momentum is eastward and Object B's momentum is northward. Use Pythagoras' theorem to find the magnitude: \[ |\vec{p}_{\text{total}}| = \sqrt{(136.0)^2 + (145.0)^2} = \sqrt{18496 + 21025} = \sqrt{39521} = 198.8 \, \text{kg} \cdot \text{m/s}. \]
05

Find the direction of the total momentum

Using trigonometry, the angle \( \theta \) can be found using \( \tan(\theta) = \frac{p_{B}}{p_{A}} = \frac{145.0}{136.0} \). Therefore, \( \theta = \tan^{-1}(\frac{145.0}{136.0}) \approx 46.7^\circ \). The angle is measured from the east towards the north.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Inelastic Collision
In an inelastic collision, two or more objects collide and move together as a single mass post-collision. This type of collision is characterized by the loss of kinetic energy, though the momentum of the system is conserved. In our scenario with objects A and B, they stick together after the collision, meaning they move as a single unit. The key point here is that the momentum, which is the product of mass and velocity, remains the same before and after the collision. This principle of momentum conservation holds true regardless of the collision being elastic or inelastic. Understanding inelastic collisions is crucial in physics because it applies to real-world incidents, such as car crashes, where two entities might become deformed and entangled, yet their total momentum is unchanged.
Vector Addition
When dealing with the momentum of objects moving in different directions, vector addition is a crucial concept. Momentum is a vector, which means it has both magnitude and direction. In the exercise, object A is moving due east, while object B is moving due north. To find the total momentum after they collide, we need to add these momentum vectors together. This is done by placing the vectors tail to tail and resolving them into their components. The overall momentum vector is found by calculating the resultant vector, which is the vector that connects the start of the first vector to the end of the last. This vector addition method allows for the conservation of momentum to be visually demonstrated and calculated mathematically.
Pythagorean Theorem
The Pythagorean Theorem is a fundamental mathematical tool used to find the magnitude of a resultant vector formed by two perpendicular vectors. In the context of our exercise, after determining the momentum vectors for objects A and B, which are at right angles to each other, you can use the Pythagorean Theorem to find the magnitude of the total momentum vector. The formula you apply is \[|\vec{p}_{\text{total}}| = \sqrt{p_{A}^2 + p_{B}^2}\]where \(p_A\) is the momentum of object A and \(p_B\) is the momentum of object B. By substituting the given values into this formula, you obtain the total momentum magnitude in a straightforward manner. This theorem is convenient in physics whenever you're dealing with perpendicular components, simplifying the process of finding the combined effect of two such vectors.
Trigonometry in Physics
Trigonometry is a powerful tool used in physics to resolve vector quantities and analyze angles between different forces or motions. In our problem, after determining the magnitudes of the momentum vectors through the Pythagorean Theorem, trigonometry is used to find the direction of the resultant momentum vector. This is done by calculating the angle \(\theta\) using the tangent function, which compares the opposite side of a right triangle to the adjacent side:\[\tan(\theta) = \frac{p_{B}}{p_{A}}\]where \(p_B\) and \(p_A\) are the momenta of objects B and A, respectively. Use the inverse tangent function, \(\tan^{-1}\), to find the angle. In our exercise, this angle tells us the direction of the total momentum in relation to the eastward path of object A, revealing that the vector moves away from it at an angle of approximately 46.7 degrees toward the north. Trigonometry thus bridges the gap between vector magnitudes and their orientation in space.

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Most popular questions from this chapter

A \(50.0-\mathrm{kg}\) skater is traveling due east at a speed of \(3.00 \mathrm{m} / \mathrm{s} .\) A \(70.0-\mathrm{kg}\) skater is moving due south at a speed of \(7.00 \mathrm{m} / \mathrm{s}\). They collide and hold on to each other after the collision, managing to move off at an angle \(\theta\) south of east, with a speed of \(v_{\mathrm{r}}\). Find (a) the angle \(\theta\) and (b) the speed \(v_{f},\) assuming that friction can be ignored.

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Multiple-Concept Example 7 deals with some of the concepts that are used to solve this problem. A cue ball (mass \(=0.165 \mathrm{kg}\) ) is at rest on a frictionless pool table. The ball is hit dead center by a pool stick, which applies an impulse of \(+1.50 \mathrm{N} \cdot \mathrm{s}\) to the ball. The ball then slides along the table and makes an elastic head-on collision with a second ball of equal mass that is initially at rest. Find the velocity of the second ball just after it is struck.

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