I'm taking a grade 11 physics correspondence course and would like to know if I am on the right track.
At the instant a tracffic light turns green, a car starts from rest and acccelerates uniformly at a rate of 4.0m/s. At the same instant, a truck travelling with a constant velocity of 90.0 km/hour overtakes and passes the car.
a. how far beyond the starting point is the car after 10.0 s?
b. how far beyond the starting point is the truck after 10 s?
c. The car passes the truck at a distance of 312.5 m beyond the starting point. How fast is the car travelling at this instant?
Equations i'm using are: distance =(vi)(t) + (0.5)(a)(t^2)
The Attempt at a Solution
Here is what I have so far.
a. d=(vi)(t) + (0.5)(a)(t^2)
=(0m/s)(10s) + (0.5)(4.0m/s^2)(10s^2)
=200 m for the car after 10 s
b. distance = (constant velocity) (time)
= 250 m for the truck after 10 s
c. I have worked out a calculation but my answer doesn't make sense
=15.6 s for the car to go 312.5 m
from this i calculated the speed
=20 m/s then i translated into km and got 72 km/hour. However I know this is wrong because logically if the car is passing the truck it would be a number greater than 90.0 km/h. What concept am I missing here???
Thanks for your help.