Download Drop of a Bullet

Work and Energy
5. What is a force?
a. change in speed over time
b. the tendency to resist change in
motion
c. a push or pull
d. apparent weightlessness
Work and Energy
5. What is a force?
a. change in speed over time
b. the tendency to resist change in
motion
c. a push or pull
d. apparent weightlessness
Work and Energy
9. What is the result of a net force
acting on an object?
a. the object will accelerate
b. the object remain motionless
c. the object’s velocity will not change
d. inertia is greater than net forces
Work and Energy
9. What is the result of a net force
acting on an object?
a. the object will accelerate
b. the object remain motionless
c. the object’s velocity will not change
d. inertia is greater than net forces
Work and Energy
Which of the following does NOT
represent work being done.
a. You lift a 4 kg box 1.5 m to the table.
b. You pull a wagon 10 meters.
c. You hold the door open for your
mom.
d. You push a desk across the floor.
Work and Energy
Which of the following does NOT
represent work being done.
a. You lift a 4 kg box 1.5 m to the table.
b. You pull a wagon 10 meters.
c. You hold the door open for your
mom. Why?
d. You push a desk across the floor.
Work and Energy
Which of the following does NOT
represent work being done.
c. You hold the door open for your
mom. Why?
Even though you apply force to to keep
the door open, the door does not
move.
Work and Energy
The amount of work done in a
specified amount of time is called
a. joules
b. resistance
c. power
d. Mechanical advantage
Work and Energy
The amount of work done in a
specified amount of time is called
a. joules
b. resistance
c. power
d. Mechanical advantage
Work and Energy
An object that is only acting under the
influence of gravity is ___________
a. decelerating
b. in free fall
c. stationary
d. weightless
Work and Energy
An object that is only acting under the
influence of gravity is ___________
a. decelerating
b. in free fall
c. stationary
d. weightless
Work and Energy
For every force there is an equal and
opposite reaction force is
a. Newton's 1st Law of Motion
b. Newton's 2nd of Motion
c. Newton's 3rd Law of Motion
d. Newton's 4th Law of Motion
Work and Energy
For every force there is an equal and
opposite reaction force is
a. Newton's 1st Law of Motion
b. Newton's 2nd of Motion
c. Newton's 3rd Law of Motion
d. Newton's 4th Law of Motion
Work and Energy
What is the gravitational acceleration
constant on earth?
a. 9.8 m/s
b. 98 m/s
c. 9.8 m/s2
d. 982 mph
Work and Energy
What is the gravitational acceleration
constant on earth?
a. 9.8 m/s
b. 98 m/s
c. 9.8 m/s2
d. 982 mph
Drop of a Bullet
Work and Energy
Which state of matter is completely
compressed, retains its shape, and
represents the lowest form of
kinetic energy among its
molecules?
Drop of a Bullet
Work and Energy
Which state of matter is completely
compressed, retains its shape, and
represents the lowest form of
kinetic energy among its
molecules?
solids
Drop of a Bullet
Work and Energy
What is the equation for calculating kinetic
energy?
Drop of a Bullet
Work and Energy
What is the equation for calculating kinetic
energy?
KE = ½ mv2
OR
mv
KE=
2
2
Drop of a Bullet
Work and Energy
Kinetic energy is expressed in what units?
Drop of a Bullet
Work and Energy
Energy is measured in what units?
Joules
J
Drop of a Bullet
Work and Energy
What is the kinetic energy of a 5kg object
traveling at 10m/s?
Drop of a Bullet
Work and Energy
What is the kinetic energy of a 5kg object
traveling at 10m/s?
KE = ½ mv2
KE = 5kg x (10m/s)2
2
= 250 J
Drop of a Bullet
Work and Energy
What is the equation for calculating
gravitational potential energy?
Work and Energy
What is the equation for calculating
potential energy?
PE = mgh
What do the letters stand for?
Work and Energy
What is the equation for calculating
potential energy?
PE = mgh
What do the letters stand for?
m = mass g = gravity (9.8m/s2)
h = height of the object in m
Drop of a Bullet
Work and Energy
A 1.5 kg coconut hangs in a palm tree?
How much gravitational potential energy
does the coconut have if the tree is 15
meters tall?
Drop of a Bullet
Work and Energy
A 1.5 kg coconut hangs in a palm tree?
How much gravitational potential energy
does the coconut have if the tree is 15
meters tall?
PE = mgh
= (1.5 kg)(9.8m/s2)(15 m)
220 J
Drop of a Bullet
Work and Energy
A rollercoaster car with a mass of 500 kg
has 600 J of potential energy. How tall is
the rollercoaster?
PE
h
PE = mgh so gm
= 600 kJ/(9.8m/s2 x 500kg)
= 122 m
Drop of a Bullet
Work and Energy
What is the mechanical energy of a 40 kg
child swinging at the moment her velocity
is 20 m/s and she is 2 m off of the
ground?
Drop of a Bullet
Work and Energy
What is the mechanical energy of a 40 kg
child swinging at the moment her velocity
is 20 m/s and she is 2 m off of the
ground?
Hint: Mechanical Energy = KE + PE
Calculate each and sum.
Drop of a Bullet
Work and Energy
Calculate the mechanical energy of a 40 kg
child swinging at the moment her velocity
is 20 m/s and she is 2 m off of the
ground?
Hint: Mechanical Energy = KE + PE
 mv 2 

   mgh 
 2 
Drop of a Bullet
Work and Energy
Calculate the mechanical energy of a 40 kg
child swinging at the moment her velocity
is 20 m/s and she is 2 m off of the
ground?
Hint: Mechanical Energy = KE + PE


m 2
40
kg

20

s

2



2


  40kg  9.8 m s 2  2m  8784 J




Drop of a Bullet
Work and Energy
What is the mechanical energy of a 40 kg
child swinging at the moment her velocity
is 20 m/s and she is 2 m off of the
ground?
PE = mgh so
PE
h
= 600 kJ/(9.8m/s2 x 500kg)gm
= 122 m