If a car travels 45 m in 7 seconds then it travels 65 m for

If a car travels 45 m in 7 seconds, then it travels 65 m for 10 seconds, then slows down to a stop in another 2 seconds, find the average speed? Smart Suzie walks at a constant 4 m/s for 30 s, then stops for 10 s, than continues at a constant 3 m/s for another 12s. What is Suzie\'s average speed? (Do you have enough information to find her distances?)

Solution

b)

Total Distance covered = Distance covered in

i) 30s at a speed of 4m/s +

ii) 0m in 10s +

iii) 12s at a speed of 3m/s

Total Distance = 30(4) + 0 + 12(3) = 120 + 0 + 36 = 156m.

total time = 30s + 10s + 12s = 52s

Average speed = total distance / total time = 156/52 = 3m/s.

a)

car travels 45m in 7s and then 65m in 10s and then stops in two seconds.

Before the car stops speed of car = 65/10 = 6.5 m/s

Hence decelaration = 6.5 / 2 = 3.25m/s²

Distance travelled while the car is stopped = v² / 2a = (6.5*6.5) / (2*3.25) = 6.5m

Hence, total distance travelled = 45 + 65 + 6.5 = 116.5

Total time = 7 + 10 + 2 = 19s

Average Speed = Total distance / total time = 116.5 / 19 = 6.1316 m/s