Equations for accelerated motion

Question

A car starts from rest and reaches the speed of 10 m/s in 30s. assuming the car accelerates at a constant rate, what can you determine about the motion of the car from this info? what can't you determine?

my teacher's answers states that you can't find direction and final position, however you can find the displacement which is 150 after plugging into the formula. Why can we find the displacement when you can't find the final position? I thought that displacement is final position - intial position?

please explain to me the difference between displacement (delta), x final, x initial.

thank you

Answer 1

You can't find the final position because the start position was never given. A displacement of 150 m could take place by starting at x=0 and ending at x=150, but it could also have occurred by starting at x=20 and ending at x=170. A difference of position by 150 (displacement) is definitely known, but the start and end points of that 150 meter length are unknown.

Answer 2

Displacement is a vector, which means it has magnitude and direction. If you can't find both, then you can't find displacement. What you can find in the example given is the magnitude of displacement (150 m after 10 sec), but not its direction.

Similarly velocity is a vector, for which you can find the magnitude (10 m/s after 10 sec) but not the direction.

When we use the word speed we are talking about the magnitude of velocity.

Final position is also a vector quantity (at least it is for anyone not living in a one dimensional world).