a. Explanation Given data: Mass of the elevator ( m ) is 1000 kg. Change in the height of the elevator ( Δ y ) is 100 m. Elevator motor lifts the elevator at a constant speed. Formula used: Write the expression for work energy equation for the given conditions as follows. W = Δ K + Δ U g + Δ E th (1) Here, Δ K is the change in the kinetic energy, Δ U g is the change in the gravitational potential energy, and Δ E th is the change in the thermal energy. Write the expression for change in the gravitational potential energy. Δ U g = m g Δ y (2) Here, m is the mass of the object, g is the acceleration due to the gravity, which is 9.8 m s 2 , and Δ y is the change in height. Explanation: As the motor lifts the elevator at a constant speed, the change in the kinetic energy is zero. From the given data, the thermal energy is not generated in the system. Therefore, the change in the thermal energy is zero for the given system. Modify the expression in equation (1) by substituting the 0 J for Δ K , and 0 J for Δ E th as follows. W = 0 J + Δ U g + 0 J W = Δ U g (3) Calculation of change in the gravitational potential energy: Substitute 1000 kg for m , 9 b. To determine To find: The power supplied by the motor to lift the elevator for 50 s at constant speed.

College Physics: A Strategic Approach (3rd Edition)

3rd Edition

ISBN: 9780321879721

Author: Randall D. Knight (Professor Emeritus), Brian Jones, Stuart Field

Publisher: PEARSON

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Instantaneous Power

Power is defined in physics as the amount of energy transmitted or transformed per unit time. The watt is the unit of electricity in the International System of Units, equivalent to one joule per second.

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Chapter 10, Problem 46P

To determine

To find: The amount of work done by the elevator motor to lift the elevator at constant speed.

To determine

To find: The power supplied by the motor to lift the elevator for 50 s at constant speed.

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Chapter 10, Problem 45P

Chapter 10, Problem 47P

Chapter 10 Solutions

College Physics: A Strategic Approach (3rd Edition)

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The amount of work done by the elevator motor to lift the elevator at constant speed.

Solution Summary: The author explains that as the elevator motor lifts at a constant speed, the change in the kinetic energy is zero.

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To find: The amount of work done by the elevator motor to lift the elevator at constant speed.

To find: The power supplied by the motor to lift the elevator for 50 s at constant speed.

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