8. a car travels at a constant velocity of 70 mph for one hour. by the end of the second hour, the car’s velocity was 60 mph. at the end of the third hour, the car’s velocity was 80 mph. during which hour was their acceleration positive? during which hour was their acceleration negative?

  Positive acceleration is in third hour and negative acceleration is in second hour.

Explanation:

  Velocity of car in first hour =  70 mph

  Velocity of car in second hour = 60 mph

  Velocity of car in third hour = 80 mph

   Acceleration = Change in velocity / Time

   Acceleration in second hour = (60 - 70)/1 = -10 mph²

   Acceleration in third hour = (80 - 60)/1 = 20 mph²

   So positive acceleration is in third hour and negative acceleration is in second hour.

snell's law

refractve index = sin incidence / sin refraction