A car traveled at a constant velocity of 70 mph from noon to 2:00 pm. At 3:00 pm the velocity of the car was 80 mph, finally at 4:30 pm the velocity of the car was 40 mph. What is the acceleration of the car between 3:00 and 4:30 pm?

1 Answer
A08
Apr 15, 2016

#-26.bar 6 " miles.hour"^-2#
#-ve# sign shows that it is retardation.

Explanation:

Stage 1.

The car travels from noon (12.00) to 2.00 pm at constant velocity of 70mph.

Stage 2.

The car travels from noon 2.00 pm to 3.00 pm. Velocity at 3 pm was of 80mph.

As the velocity has increased the car was accelerated during this period. However, details about the kind of acceleration and its duration during this 60 minute period are not given.

Stage 3.

The car travels from noon 3.00 pm to 4.30 pm. Velocity at 3 pm was of 80mph and at 4.30 pm was 40 mph.
As the velocity has decreased during this time interval, the car was retarded during this period.

Assuming constant retardation during the period of interest and therefore, using applicable kinematic equation
#v=u+at#
#40=80+axx1.5#, rearranging and solving for #a#
#1.5a=40-80#
#a=-40/1.5=-26.bar 6 " miles.hour"^-2#
#-ve# sign shows that it is retardation.

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