A particle on the x-axis is moving to the right at 2 units per second. At a certain instant it is at the point (5,0). How rapidly it the distance between the particle and the point (0,9) on the y-axis changing at that instant

dr/dt = 1.94 units per second

Explanation:

A particle is moving on the x-axis to the right at 2 u/s.

To know how is changing the distance of the particle respect to the point (0,9), on the y-axis, you first take into account that the distance between charge and a point over the y-axis is given by:

         (1)

Next, you calculate implicitly the derivative of the equation (1) respect to t:

      (2)

Next, you solve the previous equation for dr/dx:

      (3)

dx/dt: the speed of the particle on the x-axis = 2

dy/dt: speed of the particle on the y-axis = 0

For the instant given in the statement, you have that:

x = 5

y = 9

Then, you replace the values for x, y, dx/dt and dy/dt in the equation (3):

The speed of change of the distance between particle and point (0,9) is 1.94 units per second

i think the answer is a, hope this is right, that would be my best guess.