#$&*
phy 121
Your 'cq_1_09.1' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
** CQ_1_09.1_labelMessages **
A ball accelerates uniformly as it rolls 20 cm down a ramp, starting from rest, in 2 seconds.
• What are its average velocity, final velocity and acceleration?
answer/question/discussion: ->->->->->->->->->->->-> :
v0 = 0, `ds = 20 cm, `dt = 2 seconds
v = `ds/`dt = 20/2 = 10 cm/sec
vAve = (vf+v0)/2
10cm/sec = (vf + 0)/2
vf = 20 cm/sec
a = `dv /`dt
= 20/2 = 10 cm/sec^2
#$&*
• If the time interval is in error so that it is 3% longer than the actual time interval, then what are the actual values of the final velocity and acceleration?
answer/question/discussion: ->->->->->->->->->->->-> :
then `dt = .03*2 = .06 +2 = 2.06 seconds for `dt
`ds =20cm and v0 =0
V = `dt/`dt = 20/2.06 = 9.71 cm/sec
Vf = 9.71*2 = 19.42 cm/sec and `dv = 19.42 cm/sec
A = `dv/dt = 19.42/2.06 = 9.43 cm/sec^2
#$&*
• What is the percent error in each?
answer/question/discussion: ->->->->->->->->->->->-> :
the original acceleration is 10cm/sec^2 and the actual acceleration is 9.43cm/sec^2
this is a difference of .57 cm/sec^2 / 10cm/sec^2 gives that the perecnetage is .06 or 6 percent of the original acceleration.
The original velocity is 10cm/sec and the correct is 9.71 cm/sec a difference of .29cm/sec/10 =.03 or 3 % of the original velocity
#$&*
• If the percent error is the same for both velocity and acceleration, explain why this must be so.
answer/question/discussion: ->->->->->->->->->->->-> :
no the percent for acceleration is 6% where the percent for velocity is 3% the reason is that when you find velocity you divide ds/`dt where the 3% error in time is calculated in. When you find acceleration you have `dv/`dt so you have the change in velocity which includes the first 3% error in time and divide it by the `dt which will include the 3% error in time again, doubling the percent error.
#$&*
• If the percent errors are different explain why it must be so.
answer/question/discussion: ->->->->->->->->->->->-> :
explained above
#$&*
** **
15 minutes
** **
&#Very good responses. Let me know if you have questions. &#