Download Handout Topic 2 Newton`s Laws solutions 2015

Handout Topic 2 – Newton’s Laws
1. a) State Newton’s First Law. It is commonly called ____inertia___________ ( one
word).
NEWTON’S FIRST LAW OF MOTION
An object at rest tends to stay at rest and an object in motion tends to remain in
motion with constant velocity, unless acted on by an unbalanced force (a non-zero
net force).
OR
If the net force acting on a body is equal to zero, the body will move with constant
velocity and zero acceleration.
b) Give an example:
Book resting on a table, not moving, and net force = 0
c) Explain a satellite in space, at constant velocity ,in terms of Newton’s 1 st law:
Satellite will continue in motion , theoretically forever, at present velocity, until some
force acts on it ( eg. Gravity of another planet).
d) Write the mathematical expression for net force = 0:
F 0
or
F 0 F 0
x
y
2. a) State Newton’s 2nd law and write a formula :
NEWTON’S SECOND LAW
The acceleration of an object is directly proportional to the net external force acting
on it and is inversely proportional to its mass. The direction of acceleration is in the
same direction as the net force acting on the object
F = ma
b) If you double the force what happens to the acceleration of the object?
Doubles
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c) Do the following examples. Show work.
3. a) State Newton’s 3rd law. It is commonly called ____axn___________
_____rxn___________ (two words).
NEWTON’S THIRD LAW
Whenever one object exerts a force on a second object, the second object exerts an
equal and opposite force on the first.
OR
If body A exerts a force on body B (an “action”) then body B exerts an equal and
opposite force on body A (a “reaction”). These two forces have the same magnitude
but opposite direction.
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b) Explain the following example. Draw and identify the action – reaction pairs:
Focus only on the two forces that affect the assistant’s NET FORWARD motion:
FAG – forward force on assistant exerted by ground
FAS - backward force of sled exerted on assistant.
If FAG is greater than FAS the sled will move forward ( accelerate forward).
c) Write the formula for weight and explain it:
Fg  w  mg
Weight is the force of gravitational attraction acting on a body (w = mg).
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