Why am I having trouble solving for 005 in the Velocity Dilemma 004 & 005?

[Garen]

I have solved 004 and got 12.972 as the change in velocity. I am having a little difficulty solving for 005. Initially I thought I could use the x=(1/2)(2.35)(5.52)^2+Vb(5.52) kinematics equation, but for some reason it's not right. The answer I got with my attempt was Vb =11.57559. Am I not supposed to use kinematics in this situation? What am I doing wrong?

 

[alphysicist]

Hi Garen,

I have solved 004 and got 12.972 as the change in velocity. I am having a little difficulty solving for 005. Initially I thought I could use the x=(1/2)(2.35)(5.52)^2+Vb(5.52) kinematics equation, but for some reason it's not right. The answer I got with my attempt was Vb =11.57559. Am I not supposed to use kinematics in this situation? What am I doing wrong?

If you compare the equation you are using with the one in your book, you'll see that the unknown in that equation represents the initial velocity, which is not what you want. Do you see what to do now?