Question

A car travels for 30 minutes at 30 m/s due north. The car stops for 10 ninutes, then turns and travels for 20 minutes due south at 20 m/s. What is the average velocity of the car? What is the average speed of the car?

Answer 1

Average speed 21.67 m/s

Average velocity=8.33 m/s

Step-by-step explanation:

In order to solve this, We have to know the difference between speed and velocity.

Velocity is a vector value, so it means we have to specify the magnitud and direction, we take the displacement instead of the distance.

speed is an scalar value, we only care about the magnitud, we take in count the total distance.

first we have to get the total amount of time

Total time= 30min+10min+20min=60min

Total time is= 3600 seconds

the distance on the first trame is:

`X1=v*t\\\\X1=30m/s*(30min)(60sec/1min)\\X1=54km`

the distance on the second trame is:

`X2=v*t\\\\X2=20m/s*(20min)(60sec/1min)\\X2=24km`

The total distance is the sum of both values

Td=78km

the Displacement is the vectorial sum of them, because the second trame is opposite the first, we have to substract the second distance

D=54-24=30km

`Speed(avg)=(distance)/(time) \\\\Speed(avg)=(78000m)/(3600) \\\\Speed(avg)=21.67 m/s`

`Velocity(avg)=(displacement)/(time) \\\\Velocity(avg)=(30000m)/(3600) \\\\Velocity(avg)=8.33 m/s`