HOA
EXTENSION EXERCISE 6.1
If a car of mass 800 kg is
having same kinetic energy,
what will be its speed?
Page
153
Answers
Answer:
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Explanation:
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Answer:
For an object with mass m and speed v, the kinetic energy is defined as
K =
1
2mv2
(6.1)
Kinetic energy is a scalar (it has magnitude but no direction); it is always a positive
number; and it has SI units of kg · m2/ s
2
. This new combination of the basic SI units is
known as the joule:
1 joule = 1 J = 1 kg·m2
s
2 (6.2)
As we will see, the joule is also the unit of work W and potential energy U. Other energy
units often seen are:
1 erg = 1 g·cm2
s
2 = 10−7
J 1 eV = 1.60 × 10−19 J
6.1.2 Work
When an object moves while a force is being exerted on it, then work is being done on the
object by the force.
If an object moves through a displacement d while a constant force F is acting on it, the
force does an amount of work equal to
W = F · d = F d cos φ (6.3)
where φ is the angle between d and F.
Work is also a scalar and has units of 1 N · m. But we can see that this is the same as
the joule, defined in Eq. 6.2.