15 Questions
What is the product of an external force acting on an object and the displacement the force has caused?
Work
What happens when the external force and the object's displacement are in the same direction?
The work is positive
What is an example of negative work?
Throwing an object in the air
What is true when the external force or the object's displacement is equal to zero?
The work is zero
What is the direction of the force and displacement in riding a bicycle?
Same direction
What is the formula to find the acceleration of an object?
Force divided by mass
What is the direction of the force and displacement vectors in the positive work example?
Parallel and same direction
What is the value of cos(0) in the work equation?
Positive one
What is the angle between the force and displacement vectors in the zero work example?
90 degrees
What is the value of cos(180) in the work equation?
Negative one
What is the condition for zero work?
The external force and the displacement of the object are perpendicular to each other.
What is the unit of work in the formula W = F · d?
Joule (J)
What is the angle between the force and displacement vectors for positive work?
Between 0 and 90 degrees
What is the purpose of drawing a free-body diagram when calculating work?
To identify the directions of all forces acting on an object
What is the difference between work in physics and work in general?
Work in physics is quantitative, while work in general is non-quantitative
Study Notes
Work in Physics
- Work is defined as the product of an external force acting on an object and the displacement caused by that force.
- It measures the energy transferred to or from an object.
Types of Work
- Positive Work: When the external force and displacement are in the same direction (e.g., pushing an object on a smooth surface, riding a bicycle, kicking a stationary ball).
- Negative Work: When the external force and displacement are in opposite directions (e.g., throwing an object upward, fluid resistance to flow, pushing an object on a rough surface).
- Zero Work: When the external force or displacement is zero, or when they are perpendicular to each other (e.g., carrying a box, pushing a sturdy wall, sitting on a chair).
Work Formula
- Work (W) is a scalar quantity, measured in Joules (J) or Newtons-meter (Nm).
- The formula is: W = F · d, where F is the force vector and d is the displacement vector.
- The dot product of two vectors yields a scalar quantity.
Work and Angle
- If the angle between the force and displacement vectors is between 0 and 90 degrees, the work is positive.
- If the angle is between 90 and 180 degrees, the work is negative.
- If the angle is 90 degrees, the work is zero.
Calculating Work
- Determine the directions of the force and displacement vectors using a free-body diagram.
- Calculate the force using Newton's second law (F = ma).
- Calculate the work using the formula: W = F · d.
Examples
- Positive Work: A 2 kg ball falls from a height of 1.5 m. The force is gravitational, and the work is positive.
- Negative Work: A frictional force of 12 N acts on a box displaced by 3 m. The work is negative.
- Zero Work: A chocolate box is secured in a trolley moving at 12 m/s. The force (weight) of the box is perpendicular to the displacement, so the work is zero.
Learn about the definition of work in physics, including how it's calculated and examples of positive work. Understand the concept of energy transfer and how it relates to force and displacement.
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