The velocity of a car teduces from 30 km/h as the car approaches a stop sigh. is this an example of positive or negative accelerationthe

The stopping car has negative acceleration.

Explanation:

 We know acceleration is the rate of change of velocity. That is

            Acceleration(a) = ( Final velocity - Initial velocity )/ Time taken.

            Here Final velocity = 0 km/h( car stops) and initial velocity = 30 km/h

             So acceleration = (0-30)/time = -30/ time

             Time is always positive , so -30/time is negative, so the stopping car has negative acceleration.

one person pulls 90n one way and the other has 100n pulling the other way.

so the net force = 90 - 100 = -10n,

or the ans can be 10n if the picture shows -90n and 100n instead.