Kinetic Energy of an arrow problem

[HeavyGuy]

Homework Statement

An arrow slows down from 43 m/s to 28 m/s as it passes through an apple. If the 493-g apple was originally at rest and sped up to 0.44 m/s, what is the mass of the arrow

Vapple,i = 0 m/s
Vapple,f = 0.44 m/s
Varrow,i = 43 m/s
Varrow,f = 28 m/s
m,apple = o.493 kg
m,arrow = ?

Homework Equations

im guessing we only need Eki = Ekf which is 1/2mvi(ar)^2 + 1/2mvi(ap)^2 + 1/2mvf(ar)^2 + 1/2mvf(ap)^2

The Attempt at a Solution

i plugged it all into the equation so it looks like this near the end

924.5m = 0.0477224 + 392m

i then subtracted the 392 from 924.5 and divided that number by the long decimal to solve for m, but answer was totally off. can anyone tell me where i went wrong? thanks

 

[indietro]

i think i would approach this questions as a conservation of momentum problem rather than

 

[indietro]

I think i would approach this problem as a conservation of momentum rather than kinetic energy.
P_i = P_f
m_arv_{i ar} + m _apv_{i ap} = m_arv_{f ar} + m _apv_{f ap}

so you know the mass of the apple, both initial and final velocities of the arrow as well as both initial and final velocities of the apple!

Hope that helps!

 

[HeavyGuy]

thanks a lot! i was wondering what i was doing wrong lol