51). Average Speed =
(total distance biked) / (time to bike the distance)
= (45 km + 45 km) / (4 hours)
= (90 km) / (4 hours)
= 22.5 km/hour
Displacement =
the distance and direction from the start-point to the end-point,
no matter what the route was from start to finish.
Our biker-babe started out from home and ended up at home.
The distance between home and home is zero.
Her displacement for the whole trip is zero.
52). First, there's the little problem of how long she took
in each direction.
Return = Go + 0.5 hour
Return + Go = 4 hours
Return - Go = 0.5 hour
Add the two equations:
2 x Return = 4.5 hours
Divide by 2: Return = 2.25 hours
So Go = 1.75 hours.
(Check: Sum = 4 hours. Return is 1/2 hour more than Go. All OK.)
Now, finally . . .
Velocity = (displacement + direction) / (time)
Going: Velocity = (45 km east) / (1.75 hours)
= 25.71 km/hr east .
Returning: Velocity = (45 km west) / (2.25 hours)
= 20 km/hr west .