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The lead female character in the movie Diamonds Are Forever is standing at the edge of an offshore oil rig. As she fires a gun, she is driven back over the edge and into the sea. Suppose the mass of a bullet is \(0.010 \mathrm{kg}\) (a) What and its velocity is \(+720 \mathrm{m} / \mathrm{s} .\) Her mass (including the gun) is \(51 \mathrm{kg}\) recoil velocity does she acquire in response to a single shot from a stationary position, assuming that no external force keeps her in place? (b) Under the same assumption, what would be her recoil velocity if, instead, she shoots a blank cartridge that ejects a mass of \(5.0 \times 10^{-4} \mathrm{kg}\) at a velocity of \(+720 \mathrm{m} / \mathrm{s} ?\)

Short Answer

Expert verified
(a) Her recoil velocity is \(-0.141\) m/s; (b) with blank, it's \(-0.0071\) m/s.

Step by step solution

01

Understanding Conservation of Momentum

The principle of conservation of momentum states that when no external forces act on a system, the total momentum of the system remains constant. In this scenario, the system consists of the bullet and the woman with the gun. Initially, the total momentum is zero because both are at rest.
02

Calculating Bullet Momentum

Momentum is defined as the product of mass and velocity. For the bullet, its initial momentum is given by the formula: \[ p_{ ext{bullet}} = m_{ ext{bullet}} imes v_{ ext{bullet}} = 0.010 imes 720 \] This results in a momentum of \( 7.2 \, ext{kg} \, ext{m/s} \).
03

Applying Conservation of Momentum for Part (a)

Since the initial momentum of the system is zero, the momentum of the woman (including the gun) must be equal and opposite to that of the bullet to conserve momentum. Thus, \[ -p_{ ext{woman}} = p_{ ext{bullet}} \] Substitute \( 51 \, ext{kg} \) for her mass to find her velocity \( v \): \[ 51 imes v = -7.2 \] Solving this equation gives \( v = - rac{7.2}{51} \approx -0.141 \, ext{m/s}\).
04

Calculating Blank Momentum

Apply the same process as with the bullet. The momentum for the blank cartridge mass is calculated as: \[ p_{ ext{blank}} = m_{ ext{blank}} imes v_{ ext{blank}} = 5.0 \times 10^{-4} \times 720 \] This results in a momentum of \( 0.36 \, ext{kg} \, ext{m/s} \).
05

Applying Conservation of Momentum for Part (b)

Similarly, to the live bullet scenario, the momentum of the woman must be equal and opposite to that of the blank cartridge. Thus, \[-p_{ ext{woman}} = p_{ ext{blank}} \] Using the same mass for the woman: \[ 51 imes v = -0.36 \] Solving this equation gives \( v = -\frac{0.36}{51} \approx -0.0071 \, ext{m/s}\).

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Key Concepts

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

Physics Problem Solving
When tackling physics problems like the one involving the lead female character in "Diamonds Are Forever," the key is to break down the problem into manageable parts. Here, the main challenge is understanding the recoil effect when firing a gun, using the laws of physics to solve for unknown quantities.

To begin, identify the system and clarify the conditions. Here, the system includes the woman, her gun, and the bullet. It's crucial to recognize that initially, this system is at rest. Physics tells us that when no external force acts on such a system, the total momentum remains unchanged.

The goal in such problems is often to apply the **conservation of momentum**. This principle states that the total momentum before an event (such as firing a gun) must equal the total momentum after the event. By comprehensively understanding each component within the problem, you can substitute the known values into momentum equations and solve for unknowns, ensuring every step logically follows from the previous one.
Recoil Velocity
Recoil velocity is a fascinating aspect of physics. When a gun is fired, both the bullet and the shooter (in this case, the female character) experience forces. According to Newton's Third Law, every action has an equal and opposite reaction. When a bullet is fired forward, the gun experiences an opposite force moving it backward—this is the recoil velocity.

In the example given, the woman and her gun are initially stationary. Hence, the system's total momentum is zero. When a bullet is fired, it carries forward momentum. To conserve momentum, the woman must move backwards with a velocity that balances this out.

The recoil velocity can be calculated by balancing the momentum of the woman and gun with that of the bullet. This means setting the momentum of the bullet equal to the negative of the momentum of the woman. This, thereafter, allows you to solve for her backward velocity. Such an understanding highlights how interconnected the motion of particles and objects are in physics.
Momentum Calculation
Momentum is the product of an object's mass and its velocity. It's a key concept when solving problems involving motion, like figuring out recoil velocities. To compute momentum, use the formula:

\[ p = m \times v \]

where \( p \) is the momentum, \( m \) is the mass, and \( v \) is the velocity. In the case of the bullet fired from the gun in the original exercise, its mass and velocity determine its momentum.

Before the gun is fired, the total momentum of the system is zero, as both the gun and bullet are at rest. When the bullet is shot, it has a momentum determined by its mass and velocity. To maintain the total momentum of the system at zero, the woman and the gun recoil with an equal amount of momentum in the opposite direction.

This conservation allows us to set the momentum of the bullet equal to the opposite momentum of the woman and the gun. It's fascinating how this simple multiplication provides insights into motion dynamics in real-world scenarios. Understanding these calculations can aid in grasping more complex physics concepts.

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Most popular questions from this chapter

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