Solving Baseball Impulse and Force Problems

[jaron]

Homework Statement

a 0.144kg baseball is pitched horizontally at +38m/s. after it is hit by a bat, the baseball moves horizontally at -38m/s.

a) what impulse did the bat deliver to the ball

b) if the bat and the ball were in contact for 8.0*10^-4 seconds, what was the average force that the bat exerted on the ball?

c) find the average acceleration of the ball during its contact with the bat.

Homework Equations

J = Ft
Ft = mv1 - mv2

The Attempt at a Solution

a) Ft = mv Ft = 0.144 * -38 Ft = -5.472 kg m/s (they got -11 kg m/s)

b) F(.0008) = 5.472
F = 5.472/.0008
F = 6840 N (they got 14000 N)

c) F = ma 6840 = 0.144a a = 6840/0.144 a = 47500m/s^2 (they got 97000m/s^2)


i know i am doing something seriously wrong here but i have no idea what??

 

[cepheid]

Well, your part (a) doesn't seem to make a lot of sense. You didn't use any of the "relevant equations" that you listed. You said the impulse was equal to the change in momentum:

J = p₂ - p₁ = mv₂ - mv₁
​

So why not calculate that? What is the final momentum? What is the initial momentum? What is the difference between the two?

Your part (a) only calculates the final momentum, and multiplies it by Ft for no discernible reason.

 

[RoyalCat]

J ≡ ΔP
ΔP ≡ P_f - P_i

Your attempt at a solution makes no sense. Try using the initial momentum and final momentum to find the impulse.

Then see how the first equation is relevant to the average force.
J = F_average*Δt

 

[jaron]

wow. yeah i don't know what i was doing before
i understand it now. serious brain malfunction.

thanks for the help people