Motion from B to C:

a = 1/2 m/s^2

t = 30 s

v = 80 m/s

x = ?

Substitute into an appropriate uniform straight line motion formula and solve for x.

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Motion from A to B:

a = 1/2 m/s^2

t = 40 m/s

v = see below

u = ?

Substitute into an appropriate uniform straight line motion formula and solve for u.

Note that v is the initial velocity in the motion from B to C ...... Therefore:

Motion from B to C:

a = 1/2 m/s^2

t = 30 s

v = 80 m/s

u = ? (this is the same as the final velocity v in the motion from A to B).

Substitute into an appropriate uniform straight line motion formula and solve for u.