Asmall rock is thrown vertically upward with a speed of 27.0 m/s from the edge of the roof of a 21.0-m-tall building. the rock doesn't hit the building on its way back down and lands in the street below. ignore air resistance. part a: what is the speed of the rock just before it hits the street?
part b: how much time elapses from when the rock is thrown until it hits the street?

A. 33.77 m/s

B. 6.20 s

Explanation:

Frame of reference:

Gravity g=-9.8 m/s^2; Initial position (roof) y=0; Final Position street y= -21 m

Initial velocity upwards v= 27 m/s

Part A. Using kinematics expression for velocities and distance:

Part B. Using Kinematics expression for distance, time and initial velocity

Since it is a second order equation for time, we solved it with a calculator. We pick the positive solution.

causes

fossil fuels burn

cities become more industrialized

human population grows worldwide

b. a lightning bug, plug of grass, and a worm