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April 28, 2016

# Homework Help: physics

Posted by jo on Saturday, September 18, 2010 at 6:45pm.

Here's a physics problem. I dont care about the answer, i just want to know how to do it. dont have to be too detailed.. but i dont really kno how to start this

1.) A model rocket blasts off from the ground rising straight upward with a constant acceleration that has a magnitude of 86 m/s^2 for 1.70 seconds, at which point fuel runs out. Air resistance neglected What maximum altitude will the rocket reach?

2.)In reaching her destination, a backpacker walks with an average velocity of 1.34 m/s, due west. This average velocity of 2.68 m/s, due west,,turns around and hikes with an average velocity of 0.447 m/s due east. how far did she walk?
• physics - bobpursley, Saturday, September 18, 2010 at 7:14pm

1. Using the acceleration and time, calculate the velocity and height at fuel burnout. Then figure the height the rocket can go above this with that initial velocity. Add the heights to get the maximum altitude.

Here is a second way.
Energy put into rocket = change in PE
Force*distance=mgh
Mass*acceleration*distance= mgh
but distance= avgvelocity*time
= (Vf/2)*time=a*t^2/2
Mass*acceleration*acceleration*t^2=mgh

h= a^2/2g * t^2 where t is the time the rocket was accelerating.

check both ways.

2.Makes no sense to me.

• physics - jo, Saturday, September 18, 2010 at 7:24pm

okay. so regarding number 1. I will use the first method. So I will calculate using this formula?

x = v0t + 1/2at^2,

in which case.. x = 86(1.70) + 1/2(-10)(1.70)^2? I get x, which would be the position.. how do figure out the height over initial velocity? do i plus 0 in for v0?