you throw a rock straight up into the air with a speed of 11.5 m/s. How long does it take the rock to reach its highest point?

The acceleration of gravity is  9.8m/s²  downward.That means that if no other vertical forces but gravity act on an object, then the object's downward speed increases by  9.8m/s  every second, or its upward speed decreases by the same amount every second.So if a rock starts out moving in the upward direction at 11.5 m/s, and the only vertical force on it is the force of gravity, then it will lose 9.8 more m/s of upward speed every second, and will totally run out of upward gas after               11.5 / 9.8 = 1.173 seconds .

acceleration=a=-9.8 m/s^2Initial velocity= 11/5 m/sFinal velocity is 0 at the rock's highest pointUse the equation Final Velocity= Initial Velocity + Acceleration x TimeSubstitute values: 0= 11.5+-9.8tt= -11.5/-9.8t= 1.1735s