Question

A car travels at a constant velocity of 70 mph for one hour. At the second hour, the car’s velocity was 60 mph. At the third hour, the car’s velocity was 80 mph. At what hour was their positive acceleration? At what hour was their negative acceleration?

Answer 1

When the velocity increases, then the acceleration will be positive and when the velocity decrease then the acceleration will be negative.

During the first hour, the velocity was 70 mph and during the seconds hour the velocity was 60 mph. Hence, the velocity decrease in the seconds hour. So, the acceleration will be negative during the second hour.

Now, during the third hour the velocity increases as it is 80 mph. Hence, the acceleration will be positive during the third hour.

Answer 2

Answer:

  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.