If your solution to stated problem does not match the given solution, you should self-critique per instructions at
http://vhcc2.vhcc.edu/dsmith/geninfo/labrynth_created_fall_05/levl1_22/levl2_81/file3_259.htm.
Your solution, attempt at solution.
If you are unable to attempt a solution, give a phrase-by-phrase interpretation of the problem along with a statement of what you do or do not understand about it. This response should be given, based on the work you did in completing the assignment, before you look at the given solution.
015. Impulse-Momentum
Question: `q001. Note that this assignment contains 6 questions.
. Suppose that a
net force of 10
Your solution:
Confidence rating:
Given Solution:
The acceleration of the object will be
accel = net force / mass = 10
In 3 seconds this implies a change of velocity
`dv = 5 m/s^2 * 3 s = 15 meters/second.
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Question: `q002. By how much did the quantity m * v change during these three seconds?
What is the product Fnet * `dt of the net force and the time interval during which it acted?
How do these two quantities compare?
Your solution:
Confidence rating:
Given Solution:
Since m remained constant at 2 kg and v changed by `dv = 15 meters/second, it follows that m * v changed by 2 kg * 15 meters/second = 30 kg meters/second.
Fnet *`dt is 10
The two quantities m * `dv and Fnet * `dt are identical.
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Question: `q003. The quantity m * v is called the momentum of the object.
The quantity Fnet * `dt is called the impulse of the net force.
The Impulse-Momentum Theorem states that the change in the momentum of an object during a time interval `dt must be equal to the impulse of the average net force during that time interval. Note that it is possible for an impulse to be delivered to a changing mass, so that the change in momentum is not always simply m * `dv; however in non-calculus-based physics courses the effective changing mass will not be considered.
If an average net force of 2000 N is applied to a 1200 kg vehicle for 1.5 seconds, what will be the impulse of the force?
Your solution:
Confidence rating:
Given Solution:
The impulse of the force will be Fnet * `dt = 2000
INSTRUCTOR RESPONSE: Not a good idea, though it works in this case.
Net force = mass * acceleration.
That's where you need to start with problems of this nature.Then write an expression for the net force, which will typically include but not be limited to the force you are looking for. *&*&
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Question: `q004. If an average net force of 2000 N is applied to a 1200 kg vehicle for 1.5 seconds, what will be change in the velocity of the vehicle?
Your solution:
Confidence rating:
Given Solution:
The impulse of the 2000
impulse = Fnet * `dt = 2000
The change in momentum is m * `dv = 1200 kg * `dv.
Thus
1200 kg * `dv = 3000 kg m/s, so
`dv = 3000 kg m/s / (1200 kg) = 2.5 m/s.
In symbols we have Fnet * `dt = m `dv so that
`dv = Fnet * `dt / m.
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Question: `q005. Use the Impulse-Momentum Theorem to determine the average force required to change the velocity of a 1600 kg vehicle from 20 m/s to 25 m/s in 2 seconds.
Your solution:
Confidence rating:
Given Solution:
The vehicle changes velocity by 5 meters/second so the change in its momentum is m * `dv = 1600 kg * 5 meters/second = 8000 kg meters/second. This change in momentum is equal to the impulse Fnet * `dt, so
Fnet * 2 sec = 8000 kg meters/second and so
Fnet = 8000 kg meters/second / (2 seconds) = 4000 kg
meters/second^2 = 4000
In symbols we have Fnet * `dt = m * `dv so that Fnet = m * `dv / `dt = 1600 kg * 5 m/s / ( 2 s) = 4000 kg m/s^2 = 4000 N.
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If you understand the assignment and were able to solve the previously given problems from your worksheets, you should be able to complete most of the following problems quickly and easily. If you experience difficulty with some of these problems, you will be given notes and we will work to resolve difficulties.
Question: `q006. ‘Each time they thought they had ‘im, his engine would explode. He’d go by like they was standin’ still on Thunder Road.’ Good song. If you don’t know it you might want to look it up and listen to it (the name is 'Thunder Road'; the video is from a movie nearly 60 years old and is very dated so if it comes up, listen but don't watch it. Your imagination will create a much better picture.).
His car, including him and his load, had a mass of 2500 kg.
To escape, he had to speed up from 35 m/s to 45 m/s.
How much impulse did he need from his engine?
Your solution:
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