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Physics 1D03
Work and Kinetic Energy
•
Work by a variable force
•
Kinetic Energy and the Work-Energy Theorem
Serway & Jewett 7.3, 7.4

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Example
(massless pulleys,
no friction)
s = 2 m
How much work is done on the
rope by
F
p
? = (25N)(2m)
How much work is done by the
upward force on the ball?
= (100N)(0.5m)
100 N

Physics 1D03
Determine the work done by a force as the
particle moves from x=0 to x=6m:
x(m)
F(N)
0
1
2
3
4
5
6
5

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Then the
Work-Energy Theorem
says:
The total work done by all external forces acting on a
particle is equal to the increase in its kinetic energy.
Kinetic Energy
Definition: for a particle moving with speed v, the kinetic energy is
K = ½ mv
2
(a SCALAR)
Proof: from Newton’s Second Law, and the definition of Work.

Physics 1D03
•
Kinetic Energy is measured in joules (1J=1Nm).
•
Kinetic energy is a scalar; the work-energy theorem is a
scalar relation.
•
This theorem is equivalent to Newton’s Second Law. In

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