Total work done if it's zero?

  • #1

Homework Statement


An object is moving along some path. the total work done on the object during this process is zero.


Homework Equations


no equation


The Attempt at a Solution


A the speed of an object has decreased.
B the speed of the object may have changed.
C the object must be moving in a circle
D the velocity of the object must not have changed
E the speed of the object has not changed
F the velocity of the object may have changed

I chose answer D and E. From what I understand so far work is zero when the Force is perpendicular to the displacement.

would speed and velocity changed, when the work of an object is zero?
 

Answers and Replies

  • #2
Dick
Science Advisor
Homework Helper
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Homework Statement


An object is moving along some path. the total work done on the object during this process is zero.


Homework Equations


no equation


The Attempt at a Solution


A the speed of an object has decreased.
B the speed of the object may have changed.
C the object must be moving in a circle
D the velocity of the object must not have changed
E the speed of the object has not changed
F the velocity of the object may have changed

I chose answer D and E. From what I understand so far work is zero when the Force is perpendicular to the displacement.

would speed and velocity changed, when the work of an object is zero?
If you do no work on an object then it's kinetic energy can't change. Why do you think the velocity vector can't change if the force is perpendicular to the displacement?
 
  • #3
HallsofIvy
Science Advisor
Homework Helper
41,833
956
Note that "kinetic energy" depends upon speed, not velocity. Now, what is the difference between "speed" and "velocity"?
 
  • #4
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4,359
It there is no work being done on the object, the force acting on the object (if it exists) must be perpendicular to the velocity vector. With the force is perpendicular to the velocity vector, the direction of the velocity vector must be changing, but, with no work being done, the magnitude of the velocity (speed) must be constant.

Chet
 
  • #5
Note that "kinetic energy" depends upon speed, not velocity. Now, what is the difference between "speed" and "velocity"?
the difference between speed and velocity is that "velocity" is speed with direction, and "speed" is just direction.
 
  • #6
Doc Al
Mentor
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1,247
From what I understand so far work is zero when the Force is perpendicular to the displacement.
It's certainly true that if the force is always perpendicular to the displacement then the work done will be zero. But this problem only states that the total work done on the particle is zero.

would speed and velocity changed, when the work of an object is zero?
What does the Work-Energy theorem tell you?
 
Last edited:

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