help with motion problemz (1 Viewer)

[clicker]

A ball of mass 0.25 kg moving horizontally with a velocity of 13 ms-1 is hit with a bat. The final velocity of the ball is 19 ms-1 in the opposite direction. If the bat is in contact with the ball for 0.02 s, find the average force of the bat on the ball.

 

[Stan..]

I got F=-75N.

 

[BlackJack]

You are given mass and velocity: try dealing in momentums. The units tells you that total change in momentum is force * time.

 

[DementedDonkey]

I got -400N, but don't trust that I suck at motion and my half yearly is tomoro.. gahhh

ok what i did (so please correct me anyone who knows where i went wrong)...

into the equation v=u+at i sub'd v=-19, u=13 and t=0.02.. to find a. From this i found that a=-1600ms-2. Then sub'd into F=ma, where m=0.25 and a =-1600, to get F =-400N. the formulas and stuff seem too simple.. I dunno, someone let me know aye?!

 

[rama_v]

I got -400 as well. Dontyou just reverse the vectors (so that means the velocity was 32 m/s left) and then calculate a using (v-u)/t and then sub into f=ma?

 

[DementedDonkey]

im not sure about the 32ms-1 left thing... say the ball was initially travelling to the right, wouldnt you minus the vectors with the change in direction not add them? (ie, 13-19?).. nah that'd be displacement or something aye? I dont know i hate motion so much, and suck at it. Had my half yearly today, don't know why i studied, or did all of the homework for both topics.. or cared at all, cos there's no chance ill pass it.

 

[rama_v]

13--19 = 32....I think thats this question works.

 

[DementedDonkey]

hmmm... i'm not sure. I have a feeling that you cant just do that with velocities..but hey for some reason we got the same answer.... im totally lost, this is the point where i check the answer in the back of the book

 

[billeh]

13--19 = 32....I think thats this question works.

No! You're wrong u dumb@$$ . . u cant add things like that! to do it properly, u gotta relax . . have a little think, and things will come to you BIG head of yours!!!!

 

[rama_v]

Sorry for confusion

lol sorry I haven't donr those problems in a while, thats prelim stuff. Sorry every1 for the confusion I better butt out