Dynamics & Statics: Find Time for 5km Car Trip

[herbgriffin]

Homework Statement

A car starts from rest and accelerates uniformly at the rate of 1m/second square to reach a maximum speed of 60kmph. It then travels at this speed for some time and finally decelerates at a uniform rate of 0.5 m/second square to come to rest. If the total distance traveled is 5km, determine the total time taken for the car to cover this distance.

Homework Equations

The Attempt at a Solution

 

[jmb88korean]

First break this into three parts of acceleration, constant speed, and decceleration. Change the 60km/hr into meters per second to get uniform units. Knowing the final velocity, the acceleration and the initial velocity of zero, use vf= v(initial) + at to find the time for the first part. Do the same with the third part of the trip, but use a=-.5, vf=0 and vi=whatever 60km/hr is. Now for both parts use the equation x= vi + .5at^2 with x being distance. Plug in the respective values for each equation to find the distance of the third and first parts of the trip. Now subtract these from the total distance of 5 km and use the constant velocity of whatever 60km/hr in meters per second is to get time. Finally add all the times together.