All Work and No Play
Learning Goal: To be able to calculate work done by a constant force directed at different angles relative to displacement
If an object undergoes displacement while being acted upon by a force (or several forces), it is said that work is being done on the object. If the object is moving in a straight line and the displacement and the force are known, the work done by the force can be calculated as
where W is the work done by force
on the object that undergoes displacement 
directed at angle θ relative to .
Note that depending on the value of cosθ , the work done can be positive, negative, or zero.
In this problem, you will practice calculating work done on an object moving in a straight line. The first series of questions is related to the accompanying figure.
A) The work done by force
is
=> It is zero
B) The work done by force
is
=> It is positive
C) The work done by force
is
=> negative
D) The work done by force
is
=> positive
E) The work done by force
is
=> negative
F) The work done by force
is
=> zero
G) The work done by force
is
=> positive
H) Find the work W done by the 18-newton force.
=> W= 2900 J
I) Find the work W done by the 30-newton force.
=> W= 4200 J
J) Find the work W done by the 12-newton force.
=> W= -1900 J
K) Find the work W done by the 15-newton force.
W= -1800 J
Comments ( 2 )
How do you get the answers
For the first part:
It’s just cos(theta). If theta is 90 or 270 degrees, the sign of work would be zero because cos90=0 and cos270=0. If the horizontal work is to the right, the sign would be positive. If the horizontal work is to the left, the sign would be negative.
For the sencond part:
W=F*s*cos(theta)
W=Force*distance*cos(theta)
so J)
W=12N*160m*cos(180)
W=-1900J
Hope this helps!