Download Physics Chapter 1-3 Review

Physics Chapter 4-7 Review KEY
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Terminology
Force
A measure of an object’s mass (inertia) times its acceleration.
Measured in Newtons (kg·m/s2)
Inertia
The reluctance of any object to change its state of motion.
Mass is the measure of inertia
Friction
Weight: the force of gravity on an object.
Mass and weight are proportional not equal. Objects with
great mass have great weight
A force that acts between materials that touch as they move
past each other.
Equilibrium
Net forces equal zero. Forces are balanced
(object’s motion will be unchanged)
Weight
The point at which an object in free fall stops accelerating.
Terminal velocity
(textbook)
Air resistance
The friction acting upon an object moving through the air is
called air resistance.
The sum of all forces acting on an object
Net forces
Tension
Inertia
How is it measured?
Momentum
Definition, formula
and units
Impulse
Definition, formula
and units
Impact
Definition, formula
and units
Elastic collision
Force on a string rope or cable due to and object attached to
it. Based on that object mass time its gravitational
acceleration.
Inertia is an object’s resistance to a change in motion.
Inertia is a measure of mass quantified by Kg the greater the
mass, the greater the inertia.
Momentum is inertia in motion. It is calculated by finding
the product of an objects mass multiplied by its velocity.
Formula:
p = mv
Units:
kg·m/s
Impulse is an object’s change in momentum. Generally
speaking, we will be looking at changes in velocity Ft = Δmv
Impulse is measured in units of N·s
Impact refers to force and is measured in Newtons (N).
A collision in which momentum is transferred without the
loss of kinetic energy
Inelastic collision
A collision in which objects couple upon impact. Energy is
generally lost to outside the system
Problems:
1. What is the mathematical relationship between acceleration and force?
Directly proportional
2. What is the relationship between acceleration and mass?
Inversely proportional
3. Which of Newton’s laws look at these relationships (1st, 2nd, or 3rd):
a. The fact that when you push on something, it pushes back. 3rd
b. The fact that if you slam your brakes, your body keeps moving forward 1st
c. The fact that when you throw a heavy bowling ball, it doesn’t accelerate as fast
as when you throw a tennis ball 2nd
4. Observe the two diagrams below. In the first diagram A, the angles in which the
cables are set are equal. Would the combined tension in the cables be greater or
lesser than the weight of the light? What happens to the tension as you move the
cables further apart? In the second diagram B, which cable has the greater tension?
A
B
5. Draw a free body diagram for the picture below. Label all the forces acting on it.
What is the net force on the mass if A) the mass is at rest, B) the mass is sliding
down at constant velocity and C) the mass is accelerating down the ramp?
A) ΣF = 0, no
B) ΣF = 0 , no
C) ΣF ≠ 0 , yes
6. Give the reaction for the following action forces:
a. A car hits a brick wall : The Brick wall hits the car
b. Gravity pulls a boulder to earth : Gravity pulls the earth to the boulder
c. An ice skater pushes off the rail : The rail pushes against the ice skater
7. What would the acceleration be for a cyclist with a total mass of 100 kg (including
bike) providing a 50 N forward force on the road while the road created a 10 N
frictional force on the cyclist?
a = ΣF /m = 50 N – 10 N / 100 kg = 0.4 m/s2
Plug and Chug Problems:
Explain the difference between impact and impulse:
8. Explain the difference between impact and impulse.
• Impact refers to force and is measured in Newtons (N).
• Impulse refers to change in momentum and is measured in Newtons for a
period of time (N·s).
9. What is the only way to change an object’s momentum?
Supply an outside impulse to it (force for a period of time Ft)
10.
Using the conservation of momentum, how does a rocket move in
space? Please show a diagram with relative masses.
-
m
v
=
m
v
total p before (on ground) = 0
total p after in space = 0
The mass of all the exhaust gas is extremely small compared with the mass of
the rocket, yet it has a massive velocity (negative due to opposite direction.
Conversely, the mass of the rocket is massive, with a relatively small velocity
compared to the exhaust gas. These are equal and opposite in nature, and
“cancel out” to follow the conservation of momentum.
11. A 6 kg ball moving at 3.5 m/s slams into 4 kg ball at rest. After the collision
the 6 kg ball comes to a complete stop. What is the velocity of the 4 kg ball?
m1v1 = m2v2

(6 kg)(3.5 m/s) = (4 kg)v2
v2 = 5.25 m/s
12. A car traveling 25 m/s with a mass of 300 kg rear-ends another car at rest
with a mass of 450 kg and becomes entangled. Calculate the final speed of
both cars.
m1v1 = m2v2

(300 kg)(25 m/s) = (300 kg + 450 kg)v2
v2 = 10 m/s
13. What speed was a 9.0 kg ball traveling at if a force of 50 N could stop it in 3.5
seconds?
Ft = m(v1 – v2)  (50 N)(3.5 s) = (9 kg)(0m/s – v2)
v2 = 19.4 m/s