A rock stuck in the tread of a 50.0 cm diameter bicycle wheel has a tangential speed of 3.5 0m/s . When the brakes are applied, the rock's tangential deceleration is 1.40 m/s^2 .
What is the magnitudes of the rock's angular acceleration at = 1.70 ?
1.70 what? You need to include units.
What does 3.5 0m/s mean ?
Divide tangential acceleration by radius R to get angular deceleration. You may not need the 3.5 and 1.70 numbers at all, whatever they mean.