Work, Energy, and Power Quiz

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Questions and Answers

What is the result of the scalar product of two vectors A and B?

  • A vector
  • A scalar (correct)
  • A tensor
  • A matrix

The scalar product of two vectors has a direction.

False (B)

What is the formula for the scalar product of two vectors A and B if θ is the angle between them?

A.B = |A| |B| cos θ

The dot product of vectors A and B can be computed using the formula A.B = A B cos ______.

<p>θ</p> Signup and view all the answers

Match the following terms with their correct definitions:

<p>Scalar Product = Produces a scalar from two vectors Vector Product = Produces a new vector from two vectors Angle θ = The angle between two vectors for dot product Direction = Not associated with the scalar product</p> Signup and view all the answers

What does the work done by the spring force depend on?

<p>Only on the end points of the displacement (A)</p> Signup and view all the answers

The work done by the spring force is always positive.

<p>False (B)</p> Signup and view all the answers

What is the mathematical expression for the work done by the spring force when it is compressed to displacement $x_c < 0$?

<p>Ws = -kx_c^2 / 2</p> Signup and view all the answers

What is the work done by a force when there is no displacement?

<p>The work done is zero. (B)</p> Signup and view all the answers

The work done by the spring force is represented by the area of the _____ in the force vs. displacement graph.

<p>triangle</p> Signup and view all the answers

Match the following variables with their descriptions:

<p>Ws = Work done by the spring force Fs = Spring force acting on the block kc = Constant of spring compression x = Displacement from the equilibrium position</p> Signup and view all the answers

An object can do work without any motion occurring.

<p>False (B)</p> Signup and view all the answers

What equation represents the work done by a force in the direction of displacement?

<p>W = F cos θ d</p> Signup and view all the answers

If the force applied is zero, then the work done is ___.

<p>zero</p> Signup and view all the answers

Match the following scenarios with their corresponding outcomes:

<p>A raindrop falling under gravity = Work done relating to gravitational force Weightlifter holding a mass steadily = No work done Cyclist skidding to a stop = Negative work done by friction Block on smooth table = No work done due to lack of force</p> Signup and view all the answers

What does Hooke’s law state about the spring force?

<p>It only depends on the displacement from equilibrium. (D)</p> Signup and view all the answers

The work done by a spring force in a cyclic process is non-zero.

<p>False (B)</p> Signup and view all the answers

What is the formula for potential energy (V) of a spring?

<p>V(x) = (1/2) k x^2</p> Signup and view all the answers

At maximum compression, the kinetic energy of the car is converted entirely into the potential energy of the ______.

<p>spring</p> Signup and view all the answers

Match the terms with their definitions:

<p>Conservative Force = A force that does work based on initial and final positions. Kinetic Energy = The energy of an object in motion. Potential Energy = Energy stored due to an object's position. Spring Constant = A measure of a spring's stiffness.</p> Signup and view all the answers

Flashcards

Scalar Product of Vectors

The scalar product of two vectors A and B, denoted as A.B, is defined as the product of their magnitudes and the cosine of the angle between them. It is represented as A.B = AB cos θ, where θ is the angle between vectors A and B.

Calculating Dot Product

The dot product of two vectors can be calculated by multiplying the corresponding components of the vectors and adding the results.

Meaning of Dot Product

The scalar product provides a measure of how much two vectors are aligned with each other. A larger dot product (A.B) indicates a smaller angle between them, implying more alignment.

Scalar Product Result

The result of the dot product of two vectors is a scalar quantity. This means it only has magnitude and no direction.

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Dot Product of Perpendicular Vectors

The dot product of two perpendicular vectors is zero. Since cos(90°) = 0, the entire dot product becomes zero.

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Work-Energy Theorem

The change in an object's kinetic energy is equal to the total work done on the object by the net force.

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Work (W)

The force acting on an object, multiplied by the distance the object moves in the direction of the force.

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Work done at an angle

A force acting at an angle to the direction of motion does less work than a force acting parallel to the motion.

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Zero Work

Work done by a force is zero when the displacement of the object is zero, even if the force is large.

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Who does the work?

Work is done on an object when a force causes the object to move, and work is done by an object when the object exerts a force that causes another object to move.

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Work done by spring force in a cycle

The work done by the spring force in a complete cycle (returning to the starting position) is zero.

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Spring force is conservative

The spring force depends only on the displacement from the equilibrium position (Fs = -kx), and work done by the spring force is independent of the path, only depending on the start and end positions.

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Spring potential energy formula

The potential energy of a spring is proportional to the square of the displacement from its equilibrium position (V(x) = (kx^2)/2).

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Conservation of energy in spring-mass system

In a spring-mass system, the total mechanical energy (potential + kinetic) remains constant. As the potential energy increases, the kinetic energy decreases, and vice-versa.

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Collision with a spring

In a collision, the kinetic energy of the colliding object is transformed into potential energy stored in the spring. The maximum compression of the spring occurs when all kinetic energy is converted to potential energy.

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Inverse Proportionality of Spring Force

The spring force is inversely proportional to the displacement from its equilibrium position, meaning as displacement increases, the force decreases, and vice versa.

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Work Done by Spring Force

Work done by a spring force is calculated as -1/2 * k * xm^2, where k is the spring constant, and xm is the displacement from its equilibrium position.

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Spring Potential Energy

The potential energy stored in a spring is directly proportional to the square of the displacement from its equilibrium position.

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Path Independence of Spring Work

The work done by a spring force only depends on the initial and final positions, not the path taken.

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Conservation of Mechanical Energy in Springs

The total mechanical energy of a system remains constant even if the potential and kinetic energies change. This principle is demonstrated by the conservative nature of the spring force.

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Study Notes

Work, Energy, and Power

  • The terms work, energy, and power have precise meanings in physics, differing from everyday usage.
  • Work is the product of the component of force in the direction of displacement and the displacement magnitude.
  • Work is a scalar quantity and work done can be positive or negative.
  • Work done is zero if displacement is zero, force is zero, or if the force and displacement are perpendicular.
  • Kinetic energy (KE) is the energy of motion, given by KE = 1/2 * mv² where m = mass and v = velocity.
  • The work-energy theorem states that the change in a particle's kinetic energy is equal to the net work done on it.
  • Potential energy (PE) is the stored energy of a system due to its position or configuration.
  • Gravitational potential energy is PE = mgh, where m = mass, g = acceleration due to gravity, and h = height.
  • Potential energy of a spring is PE = 1/2kx², where k = spring constant and x = displacement from equilibrium.
  • Mechanical energy is the sum of kinetic and potential energies.
  • Power is the rate at which work is done or energy is transferred, given by Power = work/time.
  • Instantaneous power is the limiting value of average power as the time interval approaches zero, calculated as P = dW/dt = F.v (where v is velocity).

Scalar Product

  • A scalar product of two vectors A and B is a scalar quantity given by: A • B = AB cos θ, where θ is the angle between A and B.
  • Geometrically, the scalar product is the product of the magnitude of one vector and the component of the other along the first.
  • Scalar product obeys the commutative and distributive laws.

Collisions

  • In collisions, the total linear momentum (m•v) is conserved (quantity that does not change).
  • Elastic collision involves no loss of kinetic energy, whereas in inelastic collisions, kinetic energy changes, and some energy may be converted to other forms (e.g., heat).

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