Consider the following descriptions of the vertical motion of an object subject only to the acceleration due to gravity. Begin with the acceleration equation a(t)equals=v primev′(t)equals=g, where gequals=minus−9.8 m divided by s squared9.8 m/s2. a. Find the velocity of the object for all relevant times. b. Find the position of the object for all relevant times. c. Find the time when the object reaches its highest point. What is the height? d. Find the time when the object strikes the ground. A softball is popped up vertically (from the ground) with a velocity of 30 m divided by s30 m/s.

a) [tex]v = v_{o} - \left(9.8\,\frac{m}{s^{2}} \right)\cdot t[/tex], b) [tex]s = s_{o} + v_{o}\cdot t - \left(9.8\,\frac{m}{s^{2}} \right)\cdot t^{2}[/tex], c) [tex]t = \frac{v_{o}}{9.8\,\frac{m}{s^{2}} }[/tex], d) [tex]t = \frac{v_{o}}{2\cdot \left(9.8\,\frac{m}{s^{2}}\right)}+\frac{\sqrt{v_{o}^{2}+4\cdot s_{o}\cdot \left(9.8\,\frac{m}{s^{2}} \right)} }{2\cdot \left(9.8\,\frac{m}{s^{2}} \right)}[/tex]

Explanation:

a) The acceleration of the object is:

[tex]a = - 9.8\,\frac{m}{s^{2}}[/tex]

The velocity function is found by integration:

[tex]v = v_{o} - \left(9.8\,\frac{m}{s^{2}} \right)\cdot t[/tex]

b) The position function is found by integrating the velocity function:

[tex]s = s_{o} + v_{o}\cdot t - \left(9.8\,\frac{m}{s^{2}} \right)\cdot t^{2}[/tex]

c) The time when the object reaches its highest point ocurrs when speed is zero:

[tex]0\,m = v_{o} - \left(9.8\,\frac{m}{s^{2}} \right)\cdot t[/tex]

[tex]t = \frac{v_{o}}{9.8\,\frac{m}{s^{2}} }[/tex]

d) The time when the object hits the ground occurs when [tex]s = 0\,m[/tex]. The roots are found by solving the second-order polynomial:

[tex]t = \frac{-v_{o}\pm \sqrt{v_{o}^{2}+4\cdot s_{o}\cdot \left(9.8\,\frac{m}{s^{2}} \right)} }{2\cdot (-9.8\,\frac{m}{s^{2}} )}[/tex]

[tex]t = \frac{v_{o}}{2\cdot \left(9.8\,\frac{m}{s^{2}}\right)} \mp \frac{\sqrt{v_{o}^{2}+4\cdot s_{o}\cdot \left(9.8\,\frac{m}{s^{2}} \right)} }{2\cdot \left(9.8\,\frac{m}{s^{2}} \right)}[/tex]

Since time is a positive variable and [tex]v_{o} < \sqrt{v_{o}^{2}+4\cdot s_{o}\cdot \left(9.8\,\frac{m}{s^{2}} \right)}[/tex], the only possible solution is:

[tex]t = \frac{v_{o}}{2\cdot \left(9.8\,\frac{m}{s^{2}}\right)}+\frac{\sqrt{v_{o}^{2}+4\cdot s_{o}\cdot \left(9.8\,\frac{m}{s^{2}} \right)} }{2\cdot \left(9.8\,\frac{m}{s^{2}} \right)}[/tex]