Aball is tied to the end of a cable of negligible mass. the ball is spun in a circle with a radius 2.00 m making 0.700 revolutions per second. what is the centripetal acceleration of the ball?

Centripetal acceleration = (speed)²/(radius) .

We know the radius.  We have to find the speed.

Speed around a circle = (circumference) / (time to go around)

The circumference of the circle is  (2 π) (radius) = 4 π meters.

We don't exactly know the time to go around.
We know that the ball goes around 0.7 times/second.
Flip that over, and you have  time to go around = second/0.7 .

So now, the centripetal acceleration is

                                   (speed)²/(radius) .

                             =  (4π meters · 0.7/sec)² / (2 meters)

                             =  (4π · 0.7 / 2)    m/s²

                             =      about        4.4 m/s²

Pe = 1/2k(x)^2  and .05n/m = .05x10^-9m = x