BAS 021 Physics I: Energy of a System

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Questions and Answers

What happens when the work done on a system is positive?

Energy is stored in the system.
Energy is conserved in the system.
Energy is transferred from the system.
Energy is transferred to the system. (correct)

When a weightlifter lowers weights, the work done by the weights on his hands is _ while the work done by his hands on the weights is _.

zero; positive
positive; zero
negative; positive
positive; negative (correct)

In the context of work done by a varying force, what is the requirement for a particle's displacement?

It can be negative only.
It can be small and variable. (correct)
It must be constant.
It must be along the y-axis.

What determines the work done by a constant force on an object?

The angle between the force and the displacement. (D) Signup and view all the answers

What is true regarding the forces acting during the weightlifter's action of lowering weights?

Forces are equal and opposite according to Newton's third law. (C) Signup and view all the answers

What characterizes work done by a conservative force?

It is independent of the path taken between two points. (C) Signup and view all the answers

What is true about the work done by a conservative force over a closed path?

It is zero. (D) Signup and view all the answers

Which of the following is NOT a conservative force?

Frictional force (C) Signup and view all the answers

If a particle moves from point O to point C with different paths, what will be the work done by gravitational force?

It will be identical regardless of the path taken. (D) Signup and view all the answers

What happens to the mechanical energy when a nonconservative force, like friction, is present?

It becomes lost as internal energy. (D) Signup and view all the answers

What happens to the final kinetic energy of a system if the net work done on it is positive?

It is greater than the initial kinetic energy (B) Signup and view all the answers

Which of the following equations represents the work done by the external force?

$W_{ext} = \frac{1}{2} m v_f^2 - \frac{1}{2} m v_i^2$ (D) Signup and view all the answers

What is the relationship between work, energy, and power in physics?

Energy is the ability to perform work, while power measures the speed of doing work. (A) Signup and view all the answers

What is true about the acceleration of the electron as it travels through the plates?

It is constant and directed forward (C) Signup and view all the answers

In the context of work done by a constant force, which factor does NOT influence the work performed?

The mass of the object being moved. (D) Signup and view all the answers

If the final speed of the electron is less than the initial speed, what can be concluded about the work done?

The work done is negative (A) Signup and view all the answers

Given that the speed of light is $3 \times 10^8 \text{ m/s}$, what is the final speed of the electron when it reaches 9.6% of the speed of light?

$2.88 \times 10^7 \text{ m/s}$ (B) Signup and view all the answers

What is the formula used to calculate work done by a constant force?

W ≡ F ∆r cos θ (C) Signup and view all the answers

Which of the following best describes the role of conservative forces?

They do not depend on the path taken for work done. (C) Signup and view all the answers

In the context of the work-kinetic energy theorem, what does $,W_{ext} = \Delta K$ signify?

The work done is equal to the change in kinetic energy (D) Signup and view all the answers

How does the distance between the plates affect the force acting on an electron?

Increasing the distance decreases the force (D) Signup and view all the answers

What unit is used to measure work in the International System of Units (SI)?

Joule (C) Signup and view all the answers

Why does a weightlifter do no work on the weights while holding them still?

There is no displacement of the weights. (C) Signup and view all the answers

Which of the following statements accurately describes the role of the electric force in the acceleration of the electron?

It is responsible for the acceleration of the electron (C) Signup and view all the answers

Which statement about energy is true?

Energy can neither be created nor destroyed. (B) Signup and view all the answers

What role does the angle θ play in the calculation of work done by a force?

It determines whether work is positive, negative, or zero. (D) Signup and view all the answers

What is the final kinetic energy of the system given initial kinetic energy was zero and final velocity is $2.88 \times 10^{7}$ m/s?

$3.78 \times 10^{-16}$ J (B) Signup and view all the answers

What is the work done on the system when lifting the book against gravity?

$3.78 \times 10^{-16}$ J (C) Signup and view all the answers

What is the expression for gravitational potential energy?

$U_g = mgh$ (D) Signup and view all the answers

Given a mass $m = 9.11 \times 10^{-31}$ kg and a net force $F = 1.35 \times 10^{-14}$ N, what is the acceleration of the mass?

$1.48 \times 10^{16}$ m/s² (A) Signup and view all the answers

If a book is lifted slowly with constant velocity, how does the kinetic energy of the system change?

Remains the same since there is no change in kinetic energy (C) Signup and view all the answers

What is the relationship between work done and gravitational potential energy in this context?

Work done equals the change in gravitational potential energy. (D) Signup and view all the answers

What value represents the net force exerted on the mass in this scenario?

$1.35 \times 10^{-14}$ N (A) Signup and view all the answers

In the equation $t = \frac{v_{x,f} - v_{x,i}}{a_x}$, what does $t$ represent?

The time interval during the motion (A) Signup and view all the answers

What happens to the gravitational potential energy when an object falls?

It increases because the height decreases. (D) Signup and view all the answers

What factors determine the gravitational potential energy of an object?

Mass of the object and its vertical height above the ground. (A) Signup and view all the answers

When lifting an object, what is true regarding work done?

The same amount of work is done regardless of the lifting method. (A) Signup and view all the answers

What is the mechanical energy of a system comprised of kinetic and potential energies?

It is constant only in a conservative force field. (B) Signup and view all the answers

What is an example of a nonconservative force?

Frictional force slowing down a sliding object. (A) Signup and view all the answers

In the context of potential energy, what does a negative work indicate?

The object is losing gravitational potential energy. (A) Signup and view all the answers

If a 2 kg book is dropped from a height of 1.4 m, what can be inferred about its change in potential energy as it falls to 0.05 m?

The potential energy change is negative. (C) Signup and view all the answers

What are the two key properties of conservative forces?

Do not depend on path and always work in a closed loop. (C) Signup and view all the answers

Flashcards

Work done by a constant force

The product of the force and the displacement in the direction of the force.

Work and energy transfer

Work represents the energy transferred to or from a system. Positive work means energy transfer into the system; negative work means energy transfer out of the system.

Work done by varying force

Calculated by integrating the force over the displacement.

Systems and multiple forces

When multiple forces act on a system, the net work done is the sum of the work done by each individual force.