A rod of length 13 meters has one end P on the x-axis and the other end Q on the y-axis. If P moves on the x-axis with a velocity of 12 meters per second, then what is the velocity of the other end Q when it is 12 meters from the origin?

buubleman
Nov 25, 2015

#1**+10 **

Assuming P = (x, 0) and Q = (0, y)

\(x^2+y^2=13^2\)

Differentiate with respect to time

\(2x\frac{dx}{dt}+2y\frac{dy}{dt}=0\)

Substitute 12 for dx/dt and for y and rearrange

\(\frac{dy}{dt}= -12\frac{x}{12}=-x\)

Use the first equation above to replace x

\(\frac{dy}{dt}=-\sqrt{13^2-12^2}=-5\)

So Q moves at 5 m/s down the y-axis.

Alan
Nov 27, 2015

#1**+10 **

Best Answer

Assuming P = (x, 0) and Q = (0, y)

\(x^2+y^2=13^2\)

Differentiate with respect to time

\(2x\frac{dx}{dt}+2y\frac{dy}{dt}=0\)

Substitute 12 for dx/dt and for y and rearrange

\(\frac{dy}{dt}= -12\frac{x}{12}=-x\)

Use the first equation above to replace x

\(\frac{dy}{dt}=-\sqrt{13^2-12^2}=-5\)

So Q moves at 5 m/s down the y-axis.

Alan
Nov 27, 2015