Objects A and B are at the origin. If object A moves to (-5 ,2 )(5,2) and object B moves to (-1 ,-8 )(1,8) over 4 s4s, what is the relative velocity of object B from the perspective of object A?

1 Answer
Mar 24, 2017

Relative velocity (approximately): color(green)(2.7)2.7 units/sec at an angle of color(green)(-68.2^@)68.2

Explanation:

Here is a graph of the resultant positions:
enter image source here

The relative displacement of BB with respect to AA is
color(white)("XXX")4 " units horizontally"XXX4 units horizontally and
color(white)("XXX")-10 " units vertically"XXX10 units vertically.

The angle of displacement (to BB relative to AA) is therefore
color(white)("XXX")arctan((-10)/4)~~-1.19028995" (radians)" ~~-68.19859051^@XXXarctan(104)1.19028995 (radians)68.19859051
(calculator used for this)

The distance from AA to BB (using the Pythagorean Theorem) is
color(white)("XXX")sqrt(4^2+(-10)^2)=sqrt(116)=2sqrt(29)" units"XXX42+(10)2=116=229 units

Since this distance was covered over a period of 44 sec.
the average speed must be (2sqrt(29))/4 " units/sec" ~~2.69258..." units/sec."

velocity is a combination of speed and angle.