How Do You Calculate Displacement in Physics Problems?

[CanadianChick]

Need Some Help With Displacement...please =)

I'm working independently on Grade 11 Physics, and ran across a displacement question I need some help with. So here goes:

1. Jessie drove north at 45km/h for 20 min, then turned West and drove at 54km/h for 27min. Finally she drove South at 18km/h for 6.4 min. Find her displacement



2. According to my notes Displacement= the difference from final position to initial position



The final answer according to the book is 28km[W 28degrees N] but I have no idea how to get this answer. Any help would be GREATLY appreciated. Thanks!

 

[jhae2.718]

Draw out the displacements (displacement=speed*time) and then find the distance between the final position and the initial position. Then use trigonometry to find the angle.

So, draw a line from the origin north for the distance specified, then from there the distance west and then from the end of that distance draw the distance south. Then find the distance between where the path ended and started.

You could also write the displacements as vectors and add them together.

 

[CanadianChick]

Great =) Very helpful, thanks for the quick reply.

So there's no way to calculate it without drawing the vectors, or using Trig?

 

[jhae2.718]

The trig is just to find the angle, and all you really need is the arctangent.

With vectors, take the arctangent of the vertical component divided by the horizontal component.

 

[CanadianChick]

Great =) thank for the help!