Homework #3 is available online at http://www.masteringphysics.com and is due on Saturday Feb 21 by 8 am [NOTE EXTRA DAY]. The handwritten homework problem is due at the start of lecture on Friday Feb 20, see https://websites.umass.edu/physics131-willocq/files/2009/02/writtenhomework3.pdf.
Free fall motion will be discussed in lecture on Wednesday, so it is recommended to work on the first 3 online problems and the written problem before attacking the last 4 online problems.
Please submit questions as a comment to this post (remember to login first to the blog, following the link on the right).
Ok. So first off, making sure this works.
Second
For the last question on HW3, i’m having some difficulty.
In class you said that the hellicopter was had a velocity that was the same as the bag, but.. i’m still kind of confused on this. I feel i should be trying to find the velocity on the bag when it hits the water. Its falling from a height of 130m, and it takes 6s to hit the ground, with an acceleration on -9.8m/s^2.. so.. i feel i should use the Vf=Vi+a(change in time) equation.. but thats not the right answer.
You do not know either the initial or final velocity of the briefcase. So any equation requiring both won’t be helpful. But you do know the vertical displacement (careful with the sign!) and the time interval, as well as the acceleration.
Those 3 pieces of information should be sufficient to find the initial velocity, and then the final velocity.
HTH.
I am not sure which equation to utilize the initial height = 130m, final height = 0m, acceleration = -9.8 m/s^2 and interval of 6 s which I know to find the initial velocity of the helicopter/briefcase. I would like to try this problem for partial credit if you can point me in the right direction.
For the villain with briefcase problem, you indeed know the vertical displacement (careful with the sign though!), the time interval and the acceleration, as you wrote.
One of the three kinematics equation should then allow you to find the initial velocity first, then you should be able to find the final velocity.
HTH.