Velocity time graph part two

So, this journey that you have taken in your car is not over. You haven’t just driven nearly 4km from home for no reason. You are picking up your friend from the train station and then you are driving back home together.

You have arrived at the train station and wait for your friend. You wait 3 minutes in total for her train to arrive and for her to find the car, to exchange greetings and so on. Then the pair of you start driving back along the same road you came on in a westerly direction to get home.

Again, you accelerate for 30 seconds at a constant rate up to 36km per hour and then you drive for 5 minutes at 36km/h and then decelerate for 30 seconds at a constant rate to 0km/h.

The points that we are going to plot are in the table below with the blue box around them. We are going to add these points to our previous velocity-time graph to show the plot of the entire journey.

Notice that the velocity travelling west is negative. We can see this in the table above as well as on the plot below.

The displacement for the second part of the journey (from 360 seconds onwards) is negative. The area under the curve for this part of the journey is highlighted below.

The displacement for this part of the journey is -3300m. This is 3300m west. Can you see how the direction is given by whether the displacement is positive or negative.

The displacement we calculated in the previous lesson was 3300m or 3300m east. In the second part of the journey the displacement we calculated was -3300m or 3300m west.

The total displacement for the journey is