Question

1 (KE, PE) An object of mass 90 lbm is projected straight upward from the surface of the earth and reaches a height of 900 ft when its velocity reaches zero. The only force acting on the object is the force of gravity. The acceleraton of gravity is g = 32.2 ft/s2 . Determine the initial kinetic energy of the object [ft·lbf], and the object’s initial velocity [ft/s].

Answer 1

Answer:

Initial kinetic energy will be 2608200 lbf-ft

Initial speed will be 240.7488 m/sec                

Explanation:

We have given height h = 900 ft

Mass of the object m = 90 lbm

Acceleration due to gravity $g=32.2ft/sec^2$

Initial kinetic energy will be equal to potential energy of the object

So kinetic energy = potential energy = mgh $=90\times 32.2\times 900=2608200\ lbf-ft$

This energy is also equal to the initial kinetic energy

So $\frac{1}{2}mv^2=2608200$

$v=240.7488m/sec$

So initial velocity will be 240.7488 m/sec