I'm (almost) unstoppable!
Momentum & energy & polar bears, oh my!
Let's not be impulsive
N.R.G.
That's so random
100
Which of the following athletes has the most momentum?
A. a 62 kg junior running at 2 m/s
B. a 45 kg freshman running at 4 m/s
C. a 51 kg sophomore running at 3 m/s
D. a 75 kg senior at rest
A = 124 kg*m/s
B = 180 kg*m/s
C = 153 kg*m/s
D = 0
100
The object's kinetic energy at point C is less than its kinetic energy at point ____.
B
100
Which balloon experiences the greatest momentum change? Both started from rest.
Balloon B.
100
T/F: Kinetic energy is a scalar quantity.
True! Velocity is squared.
100
The graph below shows the motion of a car. What occurs at 4.0 s?
the car starts moving towards 0 meters
200
What are the standard units of momentum?
kg*m/s or N*s
200
How will the speed of the red cart after the explosion compare with the speed of the blue cart?
The red cart will move with half the speed of the blue cart.
200
If a 5-kg object experiences a 10-N force for a duration of 0.10-second, then what is the momentum change of the object?
Momentum Change = 1.0 kg*m/s
Momentum change is equivalent to impulse.
200
T/F: Moving objects cannot have potential energy.
False!
200
Describe a possible scenario that could apply to this graph.
the object is speeding up in the positive direction
300
How fast would a 1-kg chihuahua have to be moving to have the same momentum as a 2,000-kg bus moving at 15 m/s?
30,000 m/s (that's more than 67,000 mi/h!)
300
Draw a scenario that could be described by these three bar charts.
Example: a rock is loaded into a slingshot (beginning), launched straight upwards (middle), and reaches its highest point (end)
300
Greatest velocity change?
Greatest acceleration?
Greatest momentum change?
Greatest Impulse?
All Case A
300
T/F: An object has a kinetic energy of 40 J. If its mass were twice as much, then its kinetic energy would be 80 J.
True!
300
The physics student pulls on a rope with 500 N in both cases. Which pulls harder in response, the wall or the elephant?
Both the same - Newton's third law:
400
A car possesses 20 000 units of momentum. What would be the car's new momentum if ...
a. its velocity was doubled.
b. both its velocity was doubled and its mass was doubled.
a. p = 40 000 units (doubling the velocity will double the momentum)
b. p = 80 000 units (doubling the velocity will double the momentum and doubling the mass will also double the momentum; the combined result is that the momentum is doubled twice -quadrupled)
400
If a ball is projected upward from the ground with ten units of momentum, what is the momentum of recoil of the Earth? ____________ Do we feel this?
10 units. The Earth is so massive compared to the ball, however, that the change in velocity for the Earth is negligible.
400
Greatest velocity change?
Greatest acceleration?
Greatest momentum change?
Greatest Impulse?
All Case A
400
Missy Diwater, the former high-diver for the Ringling Brothers' Circus, had a kinetic energy of 12,000 J just prior to hitting the bucket of water. If Missy's mass is 40 kg, then what is her speed?
400
Draw an FBD for a football at the top of its arc after being thrown.
Only gravity!
500
A halfback (m = 60 kg), a tight end (m = 90 kg), and a lineman (m = 120 kg) are running down the football field. Which player has the greatest momentum?
Both the halfback and the tight end have the greatest momentum. The each have the same amount of momentum of 540 kg*m/s. The lineman only has 360 kg*m/s.
500
A 7-kg hiker ascends a 43.2-meter high hill at a constant speed of 1.20 m/s.
- kinetic energy change of the hiker.
- the potential energy change of the hiker.
a. zero
b. 3024 Joules
DeltaPE=mgh=7*10*43.2=3024
500
Which car experiences the greatest impulse?
The impulse is the same for each car. The impulse equals the momentum change. If the momentum change is the same for each car, then so must be the impulse.
500
A 900-kg compact car moving at 60 mi/hr has approximately 320 000 Joules of kinetic energy. Estimate its new kinetic energy if it is moving at 30 mi/hr.
80,000 Joules
500
Suppose a rescue airplane drops a relief package while it is moving with a constant horizontal speed at an elevated height. Assuming that air resistance is negligible, where will the relief package land relative to the plane?
Directly beneath the plane, B.