These are lines that intersect to form right angles. example: the formed by x-axis and the y-axis, a line with a slope of 3 and another line with a slope of -1/3, the sides of a rectangle, and the sides of a square form this kind of line or segment.

it's perpendicular lines

constant acceleration- a

constant velocity- c

no velocity or acceleration- b

explanation:

for body moving with a constant acceleration, the rate of change of displacement changes over time. this is proven by the increasing gradient of the curve (a) against time.

a body that is moving at constant velocity covers equal distances over equal periods of time, thus the straight line with a constant gradient c.

a stationary body   covers no displacement as time elapses. thus the flat line with   zero gradient.