On a straight road with the +x axis chosen to point in the direction of motion,

Question

On a straight road with the +x axis chosen to point in the direction of motion, you drive for 3 hours at a constant 20 miles per hour, then in a few seconds you speed up to 70 miles per hour and drive at this speed for 1 hour. What was the x component of average velocity for the 4-hour period, using the fundamental definition of average velocity, which is the displacement divided by the time interval? vavg, x = miles per hour Suppose instead you use the formula vavg, x = vix + vfx / 2. What do you calculate for the x component of average velocity? vavg.x = vux + vfx/2 = miles per hour Why does the formula used in part (b) give the wrong answer? That formula can only be used for projectile motion, such as a baseball that has been hit. That formula isn't valid unless vx changes at a constant rate (constant force). That formula only applies at high speeds.

Explanation / Answer

a) avg. velocity = total displacement/total time = (20*3)+(70*1)/(3+1) = 32.5 miles/hour. b) if avg. velocity = (vix + vfx)/2 = (20+70)/2 = 45 miles/hour. this doesn't match with answer of part a.

Related Questions

Navigate

• Browse (All)
• Browse O
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.