Physics year 11 Kinematics question?

Question

A car that is accelerating uniformly travels 18m in the fifth second of motion.

a) What is the acceleration of the car?
b) How far does the car travel in 10 seconds?

This sounds like an easy question, but nothing but distance and time is given. No velocity. I tried setting initial velocity to zero and final velocity to equal the acceleration and vice versa, but no results are coming. The answer to a) is 4 m/s-2, but I don t know how.

Thanks for helping!

Pope · Accepted Answer

Time 4.5 is the middle of the fifth second. At that point in time the car is traveling 18 ms⁻¹. Assuming that the car started from rest (not given), that is the change in velocity in 4.5 seconds.

acceleration = (18 ms⁻¹) / (4.5 s) = 4 ms⁻²

average velocity in 10 seconds = (10 s)(4 ms⁻²)/2 = 20 ms⁻¹
distance traveled in 10 seconds = (10 s)(20 ms⁻¹) = 200 m

oubaas · Answer

18*2 = a(5^2-4^2)
a = 36/9 = 4.0 m/sec^2
d = a/2*10^2 = 2*10^2 = 200 m

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Physics year 11 Kinematics question?

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