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Car \(A\) weighing 3200 lb and traveling north at \(20 \mathrm{mi} / \mathrm{hr}\) collides with car \(B\) weighing \(3600 \mathrm{lb}\) and traveling at \(30 \mathrm{mi} / \mathrm{hr}\) as shown. If the two cars become entangled and move together as a unit after the crash, compute the magnitude \(v\) of their common velocity immediately after the impact and the angle \(\theta\) made by the velocity vector with the north direction.

Short Answer

Expert verified
Magnitude of velocity \( v \approx 16.96 \) mi/hr, \( \theta \approx 30.2^\circ \) east of north.

Step by step solution

01

Convert Units

Convert the weights of the cars from pounds (lb) to slugs (mass units in the imperial system). Remember that weight is given by \( F = m \cdot g \) where \( g = 32.2 \). Therefore, the mass of car \( A \) is \( \frac{3200}{32.2} \approx 99.38 \) slugs, and the mass of car \( B \) is \( \frac{3600}{32.2} \approx 111.80 \) slugs.
02

Determine Initial Momenta

Calculate the initial momenta of both cars. Car \( A \)'s momentum is \( p_A = 99.38 \times 20 \), and Car \( B \)'s momentum is \( p_B = 111.80 \times 30 \), accounting for their velocities and masses. Car \( A \) is traveling north, while Car \( B \)'s direction is not specified—assuming perpendicular for maximum initial momentum impact.
03

Apply Conservation of Momentum

As momentum is conserved, the total momentum before the collision is equal to the total momentum after the collision. The momentum of the combined cars is \( (99.38 + 111.80) \cdot v \) where \( v \) is the final velocity. Set the total initial momentum equal to the final momentum to solve for \( v \).
04

Calculate the Resulting Magnitude of Velocity

Calculate \( v \) using the total momentum equations for the horizontal and vertical components separately, using \( p_A = 1987.6 \) slug-mi/hr north and assumed perpendicular momentum of \( p_B = 3354 \) slug-mi/hr (east). Thus, \( v = \sqrt{(\frac{1987.6}{211.18})^2 + (\frac{3354}{211.18})^2} \).
05

Determine the Velocity Angle

Compute the angle \( \theta \) using \( \tan \theta = \frac{\text{south momentum}}{\text{east momentum}} = \frac{1987.6}{3354} \). Solve for \( \theta = \arctan(\frac{1987.6}{3354}) \) to find the angle with respect to north.

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Key Concepts

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

Collision Analysis
Understanding a collision involves studying how objects interact when they hit each other. In our example, two cars collide, and they move together after the crash. This type of analysis is critical to determine what happens to their motion after contact. Key characteristics of this event include:
  • The cars become entangled, meaning they stick together rather than bounce apart.
  • The total momentum before and after the collision is conserved, a vital concept from physics. In a "perfectly inelastic" collision like this, the two separate objects become one unit with a new, shared velocity.
By analyzing the collision in this way, we use fundamental physics principles to predict the aftermath of such incidents, which is essential in fields like accident reconstruction and safety analysis.
Velocity Calculation
After a collision, calculating the new velocity of objects can be an intriguing task. When two cars collide and move together as one unit, we compute the common velocity based on the principle of momentum conservation.Follow these steps to find the velocity:1. **Sum each car's initial momentum:** Add the momentum vectors of car A and car B before they merge. Since they travel in different directions, consider them as components (north for car A, perpendicular for car B).2. **Use total momentum principle:** Since momentum is conserved, equate the sum of initial momenta to the final combined momentum. Use this to solve for the magnitude of the shared velocity: \ v = \sqrt{(\frac{p_A}{M})^2 + (\frac{p_B}{M})^2}\ Here, \(M\) is the total mass of the cars combined.This calculation allows us to determine how fast and in what direction both cars travel together, immediately post-collision.
Momentum Components
Momentum breaks down into components based on direction. In our example, car A's momentum is in a northward direction, while car B moves perpendicularly. Understanding these components is essential to predict post-collision outcomes.

Breaking it Down

  • **Northward Component:** Car A's momentum is straightforward, aligned with its velocity north. To find it, multiply its mass by its velocity.
  • **Perpendicular Component:** Assuming car B travels east perpendicularly adds orthogonal complexity. Calculate its momentum similarly, based on its eastward velocity.

Using These Components

By calculating each car's distinct momentum component, we combine them using Pythagorean theorem principles. This provides the total system momentum post-collision. Additionally, it lets us calculate the angle \( \theta \) of the resulting velocity:\[ \tan \theta = \frac{\text{north component}}{\text{east component}} \]Solving this gives us insights into the new trajectory angle of the entwined cars.

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Most popular questions from this chapter

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