course Phy 201 ??X???`??y????z??assignment #007
......!!!!!!!!...................................
14:57:43 Describe the flow diagram you would use for the uniform acceleration situation in which you are given v0, vf, and `dt.
......!!!!!!!!...................................
RESPONSE --> v0 and vf gives us vAve and `dv.We then take vAve of the second row and `dt off the first row to make`ds. We also take `dv from the second row and combine it with `dt off the first row to get a. confidence assessment: 3
.................................................
......!!!!!!!!...................................
14:57:57 ** We start with v0, vf and `dt on the first line of the diagram. We use vO and vf to find Vave, indicated by lines from v0 and vf to vAve. Use Vave and 'dt to find 'ds, indicated by lines from vAve and `dt to `ds. Then use `dv and 'dt to find acceleration, indicated by lines from vAve and `dt to a. **
......!!!!!!!!...................................
RESPONSE --> ok self critique assessment: 3
.................................................
......!!!!!!!!...................................
15:04:57 Describe the flow diagram you would use for the uniform acceleration situation in which you are given `dt, a, v0
......!!!!!!!!...................................
RESPONSE --> first dt and a will =`dv.Then `dv and v0 will give us vf.We then take vf on the tird line with v0 on the first line to get vAve.Then take vAve on the fourth line with `dt on the first to get `ds confidence assessment: 3
.................................................
......!!!!!!!!...................................
15:05:07 ** Student Solution: Using 'dt and a, find 'dv. Using 'dv and v0, find vf. Using vf and vO, find vave. Using 'dt and Vave, find 'ds. **
......!!!!!!!!...................................
RESPONSE --> ok self critique assessment: 3
.................................................
......!!!!!!!!...................................
15:20:37 Explain in detail how the flow diagram for the situation in which v0, vf and `dt are known gives us the two most fundamental equations of motion.
......!!!!!!!!...................................
RESPONSE --> (vf + v0)/2 give us vAve. vAve times `dt will give us `ds. If we put these two together we get one of the equations `ds=(vf+v0)/2*`dt. To get the next equation we know vf-v0=`dv. we also know that `dv/`dt =a. This gives us (vf-v0)/`dt=a. Now we can rearrange this equation by multiplying `dt from both sides. a`dt=vf-v0. If we arrange this one more time add v0 to both sides we get the other equation.vf=v0+a`dt confidence assessment: 3
.................................................
......!!!!!!!!...................................
15:21:36 **Student Solution: v0 and vf give you `dv = vf - v0 and vAve = (vf + v0) / 2. `dv is divided by `dt to give accel. So we have a = (vf - v0) / `dt. Rearranging this we have a `dt = vf - v0, which rearranges again to give vf = v0 + a `dt. This is the second equation of motion. vAve is multiplied by `dt to give `ds. So we have `ds = (vf + v0) / 2 * `dt. This is the first equation of motion Acceleration is found by dividing the change in velocity by the change in time. v0 is the starting velocity, if it is from rest it is 0. Change in time is the ending beginning time subtracted by the ending time. **
......!!!!!!!!...................................
RESPONSE --> ok self critique assessment: 3
.................................................
......!!!!!!!!...................................
15:49:14 qaExplain in detail how the flow diagram for the situation in which v0, a and `dt are known gives us the third fundamental equations of motion.
......!!!!!!!!...................................
RESPONSE --> a and `dt gives us `dv. v0 and `dv gives us vf so vf=v0+`dv=v0+a`dt. vf and v0 gives us vAve. This gives us vAve =(vf+v0)/2=(v0+(v0+a*`dt)/2)=v0+.5a`dt.By taking vAve*`dt we get `ds. This gives us `ds=vAve*`dt=(v0`dt+.5a`dt)*`dt=v0*`dt+.5a*dt^2 The final equation is `ds=v0`dt+.5a`dt^2 self critique assessment: 2
.................................................
......!!!!!!!!...................................
15:49:42 ** a and `dt give you `dv. `dv and v0 give you vf. v0 and vf give you vAve. vAve and `dt give you `ds. In symbols, `dv = a `dt. Then vf = v0 + `dv = v0 + a `dt. Then vAve = (vf + v0)/2 = (v0 + (v0 + a `dt)) / 2) = v0 + 1/2 a `dt. Then `ds = vAve * `dt = [ v0 `dt + 1/2 a `dt ] * `dt = v0 `dt + 1/2 a `dt^2. **
......!!!!!!!!...................................
RESPONSE --> ok self critique assessment: 3
.................................................
......!!!!!!!!...................................
15:53:00 Why do we think in terms of seven fundamental quantities while we model uniformly accelerated motion in terms of five?
......!!!!!!!!...................................
RESPONSE --> Because the the two that are not in it which are `dv and vAve help us understand how we get the other five quanities. confidence assessment: 2
.................................................
......!!!!!!!!...................................
15:53:30 ** ONE WAY OF PUTTING IT: The four equations are expressed in terms of five fundamental quantities, v0, vf, a, `dt and `ds. However to think in terms of meanings we have to be able to think not only in terms of these quantities but also in terms of average velocity vAve and change in velocity `dv, which aren't among these five quantities. Without the ideas of average velocity and change in velocity we might be able to use the equations and get some correct answers but we'll never understand motion. ANOTHER WAY: The four equations of unif accelerated motion are expressed in terms of five fundamental quantities, v0, vf, a, `dt and `ds. The idea here is that to intuitively understand uniformly accelerated motion, we must often think in terms of average velocity vAve and change in velocity `dv as well as the five quantities involved in the four fundamental equations. one important point is that we can use the five quantities without any real conceptual understanding; to reason things out rather than plugging just numbers into equations we need the concepts of average velocity and change in velocity, which also help us make sense of the equations. **
......!!!!!!!!...................................
RESPONSE --> ok self critique assessment: 3
.................................................
......!!!!!!!!...................................
15:58:47 Accelerating down an incline through a given distance vs. accelerating for a given time Why does a given change in initial velocity result in the same change in final velocity when we accelerated down a constant incline for the same time, but not when we accelerated down the same incline for a constant distance?
......!!!!!!!!...................................
RESPONSE --> because your still accelerating at the same speed and when your traveling a further distance your velocity is going to increase more because your traveling further confidence assessment: 3
.................................................
......!!!!!!!!...................................
15:59:09 ** If we accelerate down a constant incline our rate of change of velocity is the same whatever our initial velocity. So the change in velocity is determined only by how long we spend coasting on the incline. Greater `dt, greater `dv. If you travel the same distance but start with a greater speed there is less time for the acceleration to have its effect and therefore the change in velocity will be less. You might also think back to that introductory problem set about the car on the incline and the lamppost. Greater initial velocity results in greater average velocity and hence less time on the incline, which gives less time for the car to accelerate. **
......!!!!!!!!...................................
RESPONSE --> ok self critique assessment: 3
.................................................