Work, Energy & Power

Lifting mass at a constant speed

• Suppose you lift a mass upward at a constant speed, v = 0 & K=0. What does the work equal now?

• Since you are lifting at a constant speed, your APPLIED FORCE equals the WEIGHT of the object you are lifting.
• Since you are lifting you are raising the object a certain “y” displacement or height above the ground.

• When you lift an object above the ground it is said to have POTENTIAL ENERGY

Suppose you throw a ball upward

• What does work while it is flying through the air?
• Is the CHANGE in kinetic energy POSITIVE or NEGATIVE?
• Is the CHANGE in potential energy POSITIVE or NEGATIVE?

• GRAVITY

• NEGATIVE

• POSITIVE

• Note KE = K, PE = U; these symbols are
• used interchangeably.