Particle Dynamics - 1

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Session
Particle Dynamics - 1
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Session Opener
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Session Objective

1. Force and net force
2. Acceleration due to external force
3. Equilibrium due to external force
4. Newtons first law
5. Inertial mass
6. Inertial frame of reference
7. Newtons second law
8. Impulse
9. Forces in nature

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Force and net Force
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Force and net Force
Equilibrium state natural state of the object.
No interaction with surroundings.
Equilibrium state changes only by external
interaction
Force describes this interaction quantitatively
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Force and net Force
All forces acting on object combine to a net
(resultant) force
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Definition of equilibrium Under Force
Under action of several forces, object will be
in equilibrium under the condition
The object will still be at rest if it was at
rest or continue to move with constant velocity
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Newtons First Law
Galileos experiments with inclined planes
inferred that state of inertia of motion is a
natural state of an object
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Newtons First Law
Object tends to continue in a state of
equilibrium due to inertia
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Inertial Frame of Reference
A reference frame moving with constant velocity
with respect to an inertial frame is also
inertial.
? A frame of reference in which Newtons laws of
motion are valid is an inertial frame of reference
v constant
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Class Exercise - 1
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Solution
Hence answer is (b)
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Class Exercise - 2
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Solution
Two forces are equal and are at right angle to
each other. So the resultant is directed at an
angle q, where
So the resultant will be directed to north-east.
The body will be accelerated and move along
north-east.
Hence answer is (c)
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Class Exercise - 5
Two forces 3 N and 2 N act on an object to
produce a resultant force of 1 N. What is the
angle between the forces?
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Solution
Þ 12 32 22 2 3 2 cosq
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Newtons Second Law of Motion
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Newtons Second Law of Motion
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Newtons Second Law of Motion
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Newtons Second Law of Motion
How did the momentum of the ball change ?
For a constant mass
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Class Exercise - 3
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Solution
The body is on a horizontal plane. So it will be
accelerated along the horizontal direction. The
vertical component of the force will give zero
resultant (along with weight and normal reaction).
Thus, the effective force F cosq
Hence answer is (c)
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Class Exercise - 4
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Solution
When the body is released, it carries with it the
velocity of the vehicle. As the cause of
acceleration (in horizontal direction) ceases on
loss of contact with the vehicle, the
acceleration of m is zero. The only force acting
on it is due to gravity, equal to mg.
Hence answer is (d).
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Class Exercise - 7
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Solution
As force F acts, as shown, A pushes B, and B
pushes C (contact forces). All three bodies move
with the same acceleration a.
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Class Exercise - 8
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Solution
When the body just begins moving to the left, the
net horizontal force should be to left. So F2 ³
horizontal component of F1.
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Impulse
(Impulse momentum theorem)
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Class Exercise - 6
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Solution
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Forces of Nature
Forces in nature are gravitational, electrostatic
or nuclear in origin.
Contact force is transferred by direct contact.
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Gravity Force
A constant force acting near the surface of the
earth due to the attraction of the earth
It acts downward and is an action at a distance
force.
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Weight
When a body rests on a surface, gravity force
acts on it. The surface resists gravity force by
an equal and opposite force, which is weight
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Class Exercise - 10
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Solution
Weight mg, where g is the acceleration due to
gravity. Hence, it is an external influence. So W
will change from place to place Þ (I) is false.
The entire discussion of Newtons second law
depends on the assumption that mass is constant
and is a measure of inertia of the body Þ (II) is
true.
Hence answer is (b)
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Normal Reaction
? Normal reaction exists as long as the object
applies a force on the surface.
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Normal Reaction
? The number of normal reaction forces is equal
to the number of surfaces on which the objects
rests.
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Spring Force
Force stretches massless spring by x, spring
resists deformation, applying spring force F
(restoring force)
k force (spring) constant. k is a property of
the spring.
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Class Exercise - 9
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Solution
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