Calculating acceleration.

Question

Jane drives her car from A to B for a distance of 170 km for 2 hours. She then continues her journey to C and increases her speed to 100 km/h for 45 minutes. Calculate the acceleration of the car.

Answer 1

During the first 2 hours, the acceleration is zero since her speed is not changing.  Her speed during that time is

 

v = (170 km) / (2 hrs) = 85 km/hr

 

There is acceleration only during the time she increases her speed from 85 km/hr to 100 km/hr over a time interval of 45 min.

 

t = 45 min = 0.75 hrs

 

a = (v_f - v_i)/t = [(100 - 85) km/hr] / (0.75 hrs) = 20 km/hr²