# Question: 1 an automobile travels on a straight road for a...

###### Question details

1. An automobile travels on a straight road for a
distance d1 = 20 km at a speed s1 =

+30 km/h. Call this motion in the +x direction. It then reverses
direction and travels

a distance d2 = 50 km at a speed s2 = +60 km/h. (Note: The
quantities s1 and s2 are

both positive because they both represent the speed of the car.
“Speed” in physics is an

inherently positive quantity as it is the magnitude of the
velocity. “Velocity” in physics

is a quantity that contains both speed and direction information.
For one-dimensional

motion direction can be indicated with a “+” or “−” sign. In this
problem we would

say the velocity of the car is initially v1 = +30 km/h, and is v2 =
−60 km/h after

changing direction.)

Givens: d1 = 20 km, s1 = 30 km/h, d2 = 50 km, s2 = 60 km/h.

(a) What is the average velocity of the car during the full 70 km
trip? Work sym-

bolically to derive vavg(d1, d2, s1, s2) then calculate a numerical
result. (b) What is

the average speed? Work symbolically to derive savg(d1, d2, s1, s2)
then calculate a

numerical result.

Ans: (a) −20 km/h, (b) 47 km