2. Corvette speeds up quickly 3 NJIT Physics 1: General Motors mistakenly calls a car “fast” even it it’s only going 60 mi/hr. The ads mean that it speeds up quickly. That’s “acceleration.” 2015 Chevy Corvette Z06 2015 BMW M1 Concept Car “General Motors has released the initial performance results of 2015 Chevrolet Corvette Z06, making it the fastest car GM has ever made. The new 'vette accelerates from a full stop to 60 mph in a record-breaking 2.95 seconds.”

3. How fast does a Corvette accelerate? According to a GM ad, the 2015 Corvette “hits 60 mph in 2.95 seconds.” What is its acceleration (in m/s/s)? a.20.2; b. 10.1; c. 9.08; d. 4.532; e. none are close Car and Driver

4. Skip the answers given and create a step by step solution: 1.Sketch 2.Convert v and t to standard units: 3.List variables we know and want: vo, v, t, a=? 4.Pick the 2 physics equations: 3.Algebra: 4.Arithmetic: 5.Letter answer: Optional: Estimate the uncertainty. Comment on the numbers: 60sec=1min 1609m=1mi 2.24mi/hr=1m/s 0.0254m=1in 1.v=x/tBasic. (a isn’t involved.) If needed, v ave =(x-xo)/(t-to); v ave =(v+vo)/2 2.a=v/tBasic. (x isn’t involved.) Often: a=(v-vo)/t; 3. x=vo*t+at 2 /2Comes from Eqs. 1&2. Handy if no v. 4. v 2 =vo 2 +2axComes from Eqs. 3&4. Handy if no t.

5. Step by step solution 1.Sketch 2.Units: 1.v=60mph[(1m/s)/2.24mph]=26.8m/s 3.List variables: v, t, a=? 4.Pick equations 1.v=x/tBasic. (a isn’t involved.) If needed, v ave =(x-xo)/(t-to); v ave =(v+vo)/2 2.a=v/tBasic. (x isn’t involved.) ni Often: a=(v-vo)/t; 3. x=vo*t+at 2 /2Comes from Eqs. 1&2. Handy if no v. 4. v 2 =vo 2 +2axComes from Eqs. 3&4. Handy if no t. v=60mph v=0 0 t=2.95s Acceleration Is slope

6. Step by step answer cont. 5. Algebra:none 6.Arithmetic: a=(26.8-0)[m/s]/2.95s=9.08m/s/s 7.Answer: c. Comments: Uncertainty in speed is about 0.1%, in t is [.01/2.95]=0.3%, so a is uncertain by about 0.3%. The a is probably between 9.05 and 9.11m/s/s. The car speeds up quickly. Acceleration is important. When?

7. A reminder: Learn the stuff in chapter 2 Here’s how to do it: Don’t miss a class. Do the homework on the web – it’s good practice for the exam. Use the step by step method. Do the practice problems in the syllabus – it really is good practice. Use the step by step method.