Klint and matt decided to race go-karts down the hill at their house. the mass of matt's go-kart is 86kg. klint's cart falls apart halfway down the hill. matt's go-cart makes it all the way to the bottom in 40 seconds. if the total distance of the hill is 80 feet, what is the acceleration of his go-cart?

All we can say from the given information is that Matt's
average speed from the top to the bottom is

                (80 feet) / (40 seconds)  =  2 feet per second .

We're not told whether his acceleration was constant
all the way down.  IF it was, then we could use

                               Distance = (1/2 acceleration) x (time²).

                                      80 ft  =  (1/2 acceleration) x (40 sec)²

Divide each side
by 1600 sec² :             80 ft / 1600 sec² = 1/2 acceleration

Multiply each side
by  2:                           160 ft / 1600 sec² =        acceleration

                                            Acceleration  =  0.1 ft/sec² .   
             

Alinear relationship would look like a straight line on the graph. it could have a positive negative or 0 slope. so it could be a line potentially going in any direction but it must be perfectly straight.