A 150-g baseball is dropped from a tree 12.0 mabove the ground. Part A With what

Question

A 150-g baseball is dropped from a tree 12.0 mabove the ground.

Part A

With what speed would it hit the ground if air resistance could be ignored?

Express your answer to three significant figures and include the appropriate units.

1.12N

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Part B

If it actually hits the ground with a speed of 9.00 m/s , what is the magnitude of the average force of air resistance exerted on it?

Express your answer to three significant figures and include the appropriate units.

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1.12N

Explanation / Answer

part A) The velocity V under constant acceleration is V=gt
The height h is given in terms of time of free fall t as  
height of the tree = h=0.5gt^2

solving we get,

since t=sqrt(2h/g)
then finally  
V = g x sqrt(2h/g)
V = sqrt(2gh)
V = sqrt(2 x 12 x 9.81) = 15.344 m/s  

part B)

F(total) = F(gravity) - F(air resistance)
F(gravity)=mg and then
F(air resistance)= F(gravity) - F(total)

Using the total acceleration a then  
F(total) = ma
F(air resistance)=mg - ma=m(g-a)
Lets find a
still however using our acceleration a
V=sqrt(2ha) then a is

a= 0.5 V^2 / h finally

F(air resistance)=m( g - 0.5 V^2 / h )
F(air resistance)= 0.150x ( 9.81 - 0.5x(9)^2/12 )

solving we get,

F(air resistance)= 0.965 N

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