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Science Class 9 Notes – Work and Energy
1. Work : In physics work is defined if force applied on object displaces the object in
direc¬tion of force. Hei-e all three terms force, dis¬placement and direction of force are
important W= Force x displacement (force in direction of displacement)
Unit of work
1 Joule = 1 Newton. 1 metre
1 J= 1 Nm
When a force of 1 Newton moves a body through a distance of 1 metre in its own direction the
work done is 1 Joule.
Other units of work
1 joule = 1 N x lm = 105 dyne x 102cm = 107 erg
2. Work done by a force applied at an angle
W = component of force in the direction of displacement *, magnitude of displacement W =
Fcos0 S
Work done by a force can be positive or negative according as the value of cos 0 is positive or
negative.
(therefore, F and s, being magnitudes, are always positive)
W = +ve for 0 = acute angle W = —ve for 0 = obtuse angle
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Science Class 9 Notes – Work and Energy
1. Work : In physics work is defined if force applied on object displaces the object in
direc¬tion of force. Hei-e all three terms force, dis¬placement and direction of force are
important W= Force x displacement (force in direction of displacement)
Unit of work
1 Joule = 1 Newton. 1 metre
1 J= 1 Nm
When a force of 1 Newton moves a body through a distance of 1 metre in its own direction the
work done is 1 Joule.
Other units of work
1 joule = 1 N x lm = 105 dyne x 102cm = 107 erg
2. Work done by a force applied at an angle
W = component of force in the direction of displacement *, magnitude of displacement W =
Fcos0 S
Work done by a force can be positive or negative according as the value of cos 0 is positive or
negative.
(therefore, F and s, being magnitudes, are always positive)
W = +ve for 0 = acute angle W = —ve for 0 = obtuse angle
www.ncerthelp.com (Visit for all ncert solutions in text and videos, CBSE syllabus, note and many more)
