3. Your Logo or Name Here
• All moving objects have kinetic energy (KE), whether the motion is
translational, rotational, or even vibrational. It is energy by virtue of the
object’s motion.
To measure the kinetic energy of a body, you have to consider its
mass m and speed v. In symbol,
KE =
1
2
mv2
Kinetic Energy: Energy of Motion
3
4. Your Logo or Name Here 4
Example 1.
A 0.50 kg bowling ball rolls with a speed of 5.5 m/s. What is its KE?
Given:
m = 0.50 kg
v = 5.5 m/s
Solution:
Using the definition of kinetic energy, you have:
KE =
1
2
mv2 =
1
2
(0.5 kg)(5.5 m/s)2 = 7.6 J
The kinetic energy of the bowling ball is 7.6 J.
5. Your Logo or Name Here 5
Example 2.
What is the kinetic energy of a 45 kg cheetah running at 33 m/s ?
Given:
m = 45 kg
v = 33 m/s
Solution:
KE =
1
2
mv2 =
1
2
(45 kg)(33 m/s)2 =
1
2
(45 kg)(1,089) (m/s)2
The kinetic energy of a cheetah is 24,502.5 J.
6.
7. Your Logo or Name Here 7
Elastic potential energy is stored in any stretched or compressed
object like strings and rubber bands. The elastic potential energy PEe
stored in an object is determined by:
PEe =
1
2
kx2
where x is the distance stretched or compressed and k is the elastic
constant of the object. The elastic constant is also called force
constant and is measured in newtons per meter (N/m).
8. Your Logo or Name Here 8
Example 1.
A spring is compressed by 0.10 m from its relaxed length. What is
the elastic potential energy stored in the spring if its elastic constant is 15
N/m?
Given:
x = 0.10 m
k = 15 N/m
Solution:
Using the definition of elastic potential energy, you have:
PEe =
1
2
kx2 =
1
2
(15 N/m)(0.10)2 = 0.075 J
The elastic potential energy stored in the spring is 0.075 J.
9. Your Logo or Name Here 9
Example 2.
A spring has an elastic constant of 18 N/m. What is the elastic
potential energy when it is compressed to 0.12 m from its relaxed
length?
Given:
x = 0.12 m
k = 18 N/m
Solution:
PEe =
1
2
kx2 =
1
2
(18 N/m)(0.12)2 = 0.13 J
