Basically my teacher hands us out a review packet for physics and says to do it if we want practice...Okay I do the packet and I have it done, now my problem is that the teacher didn't give out the answers to the problems so I have no idea whether or not I did it right...so Im hoping some one will check my work before I take my midterm tomorrow. Sorry for being so troublesome. Anyways here are a few problems and my work involved. I don't know how to do those picture equations so bear with me -------------------------- 1. The height of a helicopter above ground is given by h = 3t³, where h is in meters and t is in seconds. After 2 seconds, the helicopter releases a small mailbag, How long after its release does the mailbag reach the ground. h = 3t³ h(2) = 24 m h' = 9t² v(2) = h' = (9)(2)² = 36 m/s Si 0 Sf 24m Vi -36 m/s Vf 42 m/s a 9.8 m/s² t ? I know that I have my signs placed oddly but thats how my brain works. Also I put all the information I have in the chart already from the work I get below except time. Vf² = Vi² + 2a(Sf - Si) Vf = sqrt(Vi² + 2a(Sf-Si)) Vf = sqrt((-36)² + (2)(9.8)(24)) Vf = 42 m/s Vf = Vi + at t = Vf-Vi/a t = 42+36/9.8 t = 7.96 s I think thats right but I wanna make sure. ------------------------------- 2. A 100 g bullet is fired from a rifle having a barrel 0.6 m long. Assuming the origin is placed where the bullet begins to move, the force (in Newtons) exerted on the bullet by the expanding gas is 15000 + 10000x - 25000x², where x is in meters. Determine the work done by the gas on the bullet as the bullet travels the length of the barrel. work: F(x) = 15000 + 10000x - 25000x² F(.6) = 15000 + 10000(.6) - 25000(.6)² F(.6) = 12000 N w = Fd w = (12000N)(.6N) = 7200 J Okay I think I did that problem horribly wrong because I mean its too easy and this is advanced physics. One last problem ---------------------------- A catcher "gives" with the ball when he catches a 0.15 kg baseball moving at 25 m/s. If he moves his glove a distance of 2 cm, what is the average force acating on his hand? Work Ke = (1/2)mv² Ke = (1/2)(.15)(25)² Ke = 46.87 J Ke = (1/2)(.15)(0)² (Im assuming the ball stops) Ke = 0 J w = Kef - Kei w = Fd F = w/d F = 46.87J/.02m = 2343.75 N thanks for your time...I feel really bad now asking someone to check my work.