Daniel B. answered • 01/21/21

A retired computer professional to teach math, physics

All three problems are to practice the formula

a = v²/r, hence v = √(ar), where

a is the centripetal acceleration,

v is the tangential velocity,

r is the radius of rotation.

1:

a = 20g

r = 8.9 m

v = √(ar) = √(20 × 9.81 × 8.9) = 41.8 m/s

2:

r = 400m/2π

a = 2.79 × 10-2 m/s²

v = √(ar) = √(2.79 × 10-2 × 400/2π) = 1.33 m/s

To run 400 m will take her

400m / 1.33m/s = 300 s = 5 min

3:

r = 75.3 m

a = g

v = √(ar) = √(9.81 × 75.3) = 27.2 m/s

It is possible that you are supposed to answer -27.2 m/s,

where the negative sign indicates counter clockwise rotation.

But I am not really sure why the problem statement explicitly mentions direction of the rotation.