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A woman stands on a scale in a moving elevator. Her mass is \(60.0 \mathrm{~kg}\), and the combined mass of the elevator and scale is an additional \(815 \mathrm{~kg}\). Starting from rest, the elevator accelerates upward. During the acceleration, the hoisting cable applies a force of \(9410 \mathrm{~N}\). What does the scale read during the acceleration?

Short Answer

Expert verified
The scale reads approximately 646 N.

Step by step solution

01

Understanding Forces Involved

The forces involved here include the gravitational force acting on the woman, the gravitational force acting on the elevator and scale system, and the normal force exerted by the scale on the woman, which is what the scale reads.
02

Calculate Gravitational Force

Calculate the total gravitational force acting on both the woman and the elevator system. The gravitational force is calculated as: \[ F_g = (m_{ ext{total}}) imes g = (60 + 815) imes 9.81 = 875 imes 9.81 \] where \( g = 9.81 \text{ m/s}^2 \) is the acceleration due to gravity.
03

Determine Acceleration of Elevator

Use Newton's second law to find the acceleration of the elevator. The net force \( F_{ ext{net}} \) can be expressed as: \[ F_{ ext{net}} = T - F_g \] where \( T = 9410 \text{ N} \) is the tension in the cable. Solve for acceleration \( a \): \[ F_{ ext{net}} = m_{ ext{total}} imes a \] \[ a = \frac{T - F_g}{m_{ ext{total}}} \]
04

Solve for Elevator Acceleration

Substitute the values to find the acceleration: \[ F_g = 875 imes 9.81 = 8573.25 \text{ N} \]\[ a = \frac{9410 - 8573.25}{875} \] \[ a = \frac{836.75}{875} \approx 0.956 \text{ m/s}^2 \]
05

Calculate Apparent Weight

The apparent weight is the reading on the scale, which is the normal force \( N \) on the woman. Using: \[ N = m_{ ext{woman}} imes (g + a) \] Substitute the given values: \[ N = 60 imes (9.81 + 0.956) = 60 imes 10.766 \] \[ N = 645.96 \text{ N} \]
06

Conclude with Scale Reading

Hence, the scale reads approximately 646 N when the elevator is accelerating upward.

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Key Concepts

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

Newton's laws of motion
Newton's laws of motion are the foundation of classical mechanics. They describe the motion of objects and explain how forces interact to affect motion. For this particular elevator problem, we mainly deal with Newton's second law. This law states that the force acting on an object is equal to the mass of the object multiplied by the acceleration it experiences. Mathematically, it is expressed as:\[ F = m \times a \]In the context of the elevator problem, we utilize this law to determine the acceleration of the elevator system. Understanding Newton's laws allows students to connect the effects of various forces, such as tension and gravity, on the motion of objects. Whenever you encounter a physics problem, remember to first identify all forces acting on the system. This approach helps break down complex interactions into manageable parts.
Gravitational force
Gravitational force is one of the fundamental forces of nature. It is the force of attraction between two masses. On Earth, this force gives objects weight. The gravitational force can be calculated using the equation:\[ F_g = m \times g \]where \( m \) is the mass of the object, and \( g \) is the acceleration due to gravity, approximately \( 9.81 \, \text{m/s}^2 \) on Earth. In the elevator problem, the gravitational force affects both the woman and the entire elevator system. It's crucial to calculate the total gravitational force to figure out how much force is acting against the elevator's upwards acceleration. Gravitational force is always directed towards the center of the Earth, and it is essential to consider it when analyzing motion and forces in a vertical direction.
Apparent weight
Apparent weight is how heavy an object feels, and it can change depending on the motion of the environment around it. For a person in an elevator, their apparent weight is what would be measured by a scale. It results from both their true weight due to gravity and any additional forces from acceleration.When the elevator accelerates upward, the apparent weight increases. This is because the scale must exert an additional force to counteract not only gravity but also the acceleration of the elevator. The formula for apparent weight when accelerating is:\[ N = m \times (g + a) \]where \( N \) is the normal force or apparent weight, \( g \) is the gravitational acceleration, and \( a \) is the acceleration of the elevator.In our problem, the apparent weight reflects the combined effect of gravitational pull and elevator's acceleration.
Elevator physics problem
Elevator physics problems often involve analyzing motion and forces applying Newton's laws and concepts like apparent weight. These problems are excellent for understanding how acceleration affects weight perception. In our specific problem, a woman's apparent weight is calculated while the elevator is accelerating upwards. Key elements to solve this type of problem include:
  • Calculate the gravitational force on objects within the system.
  • Determine the net force and subsequent acceleration using Newton's second law.
  • Compute the apparent weight using the formula for normal force in accelerated systems.
By organizing the given information and applying physics principles, you can solve such problems step-by-step. The understanding of how forces work in confined systems like elevators helps grasp the real-world application of classical mechanics.

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Most popular questions from this chapter

Several people are riding in a hot-air balloon. The combined mass of the people and balloon is \(310 \mathrm{~kg} .\) The balloon is motionless in the air, because the downward-acting weight of the people and balloon is balanced by an upward-acting "buoyant" force. If the buoyant force remains constant, how much mass should be dropped overboard so the balloon acquires an upward acceleration of \(0.15 \mathrm{~m} / \mathrm{s}^{2} ?\)

A person, sunbathing on a warm day, is lying horizontally on the deck of a boat. Her mass is \(59 \mathrm{~kg},\) and the coefficient of static friction between the deck and her is \(0.70 .\) Assume that the person is moving horizontally, and that the static frictional force is the only force acting on her in this direction. (a) What is the magnitude of the static frictional force when the boat moves with a constant velocity of \(+8.0 \mathrm{~m} / \mathrm{s} ?\) (b) The boat speeds up with an acceleration of \(1.6 \mathrm{~m} / \mathrm{s}^{2},\) and she does not slip with respect to the deck. What is the magnitude of the static frictional force that acts on her? (c) What is the magnitude of the maximum acceleration the boat can have before she begins to slip relative to the deck?

A duck has a mass of \(2.5 \mathrm{~kg}\). As the duck paddles, a force of \(0.10 \mathrm{~N}\) acts on it in a direction due east. In addition, the current of the water exerts a force of \(0.20 \mathrm{~N}\) in a direction of \(52^{\circ}\) south of east. When these forces begin to act, the velocity of the duck is \(0.11 \mathrm{~m} / \mathrm{s}\) in a direction due east. Find the magnitude and direction (relative to due east) of the displacement that the duck undergoes in \(3.0 \mathrm{~s}\) while the forces are acting.

A spacecraft is on a journey to the moon. At what point, as measured from the center of the earth, does the gravitational force exerted on the spacecraft by the earth balance that exerted by the moon? This point lies on a line between the centers of the earth and the moon. The distance between the earth and the moon is \(3.85 \times 10^{8} \mathrm{~m}\), and the mass of the earth is 81.4 times as great as that of the moon.

The drawing shows box 1 resting on a table, with box 2 resting on top of box \(1 .\) A massless rope passes over a massless, frictionless pulley. One end of the rope is connected to box 2 and the other end is connected to box \(3 .\) The weights of the three boxes are \(W_{1}=55 \mathrm{~N}, W_{2}=35 \mathrm{~N},\) and \(W_{3}=28 \mathrm{~N}\). Determine the magnitude of the normal force that the table exerts on box \(1 .\)

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