assignment 6

course phy 231

碛楚拏勉柬逎D魏懌G绖抝墬assignment #006

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006. Using equations with uniformly accelerated motion.

Physics I

02-06-2008

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20:16:03

`q001. Note that there are 9 questions in this assignment.

Using the equation vf = v0 + a * `dt determine the acceleration of an object whose velocity increases at a uniform rate from 10 m/s to 30 m/s in 15 seconds. Begin by solving the equation for the acceleration a, then 'plug in' your initial and final velocities. Describe your work step y step.

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RESPONSE -->

the final velocity is subtracted from the initial velocity and divided by the time interval.

vf-v0/ t

30 m/s- 10m/s / 15 sec=1.33 m/s squared.

confidence assessment: 3

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20:18:48

`q002. It wasn't necessary to use a equation to solve this problem. How could this problem had been reasoned out without the use of an equation?

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RESPONSE -->

since the velocity changed from 10 m/s to 15 m/s. and with the time already given, we could easily divide that from 20 to get the answer

confidence assessment: 3

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20:25:50

`q003. Use the equation `ds = (vf + v0) / 2 * `dt to determine the initial velocity of an object which accelerates uniformly through a distance of 80 meters in 10 seconds, ending up at a velocity of 6 meters / sec. begin by solving the equation for the desired quantity. Show every step of your solution.

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RESPONSE -->

looking at the equation, we could divide both sides by 2.

so dt= 10 s

ds=80m

vf= 6m/s

2*80 m = 160 m. 160m/ 10 s = 16

16-6m/s=10m/s

confidence assessment: 3

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20:34:48

`q005. Using the equation `ds = v0 `dt + .5 a `dt^2 determine the initial velocity of an object which accelerates uniformly at -2 m/s^2, starting at some unknown velocity, and is displaced 80 meters in 10 seconds. Begin by solving the equation for the unknown quantity and show every step.

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RESPONSE -->

.5 a `dt^2 is added to both sides. dt is then divided by both sides to get the initial velocity.

ds=80m

dt=10sec

a = -2m/s squared

we then start plugging in the numbers in the problem

80m -.5*-2m/s squared*10sec squared/10 sec

80m-(-100m)/10 sec

180/10=18 m/s

confidence assessment: 3

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20:40:45

`q007. Using the equation vf^2 = v0^2 + 2 a `ds determine the initial velocity of an object which attains a final velocity of 20 meters/second after accelerating uniformly at 2 meters/second^2 through a displacement of 80 meters. Begin by solving the equation for the unknown quantity and show every step.

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RESPONSE -->

vf squared - 2 a ds = v0 squared

both sides of the equations is squared.

vf= 20 m/s

a= 3m/s squared

ds=80 m

v0 =20 m/s squared - 2 * 2 m/s squared * 80 m=8.9m/s

confidence assessment: 2

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20:48:44

`q009. Describe in commonsense terms the motion of the object in this example if its initial velocity is indeed -8.9 m/s. Assume that the object starts at the crossroads between two roads running North and South, and East and West, respectively, and that the object ends up 80 meters North of the crossroads. In what direction does it start out, what happens to its speed, and how does it end up where it does?

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RESPONSE -->

vAve= -8.9 m/ s + 20 m/s / 2 =

5.5 m/s

80m which is the displacement of the object is divided by 5.5 m/s =14.5 s

velocity change of 28.5 m/sec / 14.5 sec = 2 m/s squared

confidence assessment: 2

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