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I throw a tennisball in the air with the velocity 8m/s. how far up can the ball come

 Oct 1, 2014

Best Answer 

 #1
avatar+23254 
+5

The formula:   y  =  -4.9t² + vt    can be used:

    y  =  height          v  =  initial velocity         t  =  time (in seconds)

    -4.9 m/sec²  reflects the acceleration due to gravity, - because it pulls downward

y  =  -4.9t² + 8t 

At  t = 0,  y = 0 and the ball begins to rise.

When  y = 0  again, the ball has fallen back down to earth.

If you can find the time when the ball again hits the ground, then at half that time, the ball will be at its maximum height. So we need to solve the equation:

    0  =  -4.9t² + 8t                    Factor this by factoriing out the t:

    0  =  t(-4.9t + 8)

So:  t = 0     and     -4.9t + 8 = 0

                              -4.9t = -8

                                    t = -8/-4.9              which is approximately  t = 1.633

Halfway between these two times, the ball will be at its maximum height  --->   t = 0.816

When  t = 0.816   --->  y = (-4.9)(0.816)² + 8(0.816)  ≈  3.3 m

 Oct 1, 2014
 #1
avatar+23254 
+5
Best Answer

The formula:   y  =  -4.9t² + vt    can be used:

    y  =  height          v  =  initial velocity         t  =  time (in seconds)

    -4.9 m/sec²  reflects the acceleration due to gravity, - because it pulls downward

y  =  -4.9t² + 8t 

At  t = 0,  y = 0 and the ball begins to rise.

When  y = 0  again, the ball has fallen back down to earth.

If you can find the time when the ball again hits the ground, then at half that time, the ball will be at its maximum height. So we need to solve the equation:

    0  =  -4.9t² + 8t                    Factor this by factoriing out the t:

    0  =  t(-4.9t + 8)

So:  t = 0     and     -4.9t + 8 = 0

                              -4.9t = -8

                                    t = -8/-4.9              which is approximately  t = 1.633

Halfway between these two times, the ball will be at its maximum height  --->   t = 0.816

When  t = 0.816   --->  y = (-4.9)(0.816)² + 8(0.816)  ≈  3.3 m

geno3141 Oct 1, 2014

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