Register to reply

Find the net force with the given position vector

by dimeloom
Tags: net force, position vector
Share this thread:
dimeloom
#1
Sep13-10, 01:04 PM
P: 2
[b]1.The position vector of a 3000N helicopter is given by:
r=(.02 m/(s^3))(t^3)i + (2.2m/s)tj - (0.06 m/(s^2))(t^2)k
Find the net force on the helicopter at t = 5s.



[b]2. I really have no clue where to begin.



[b]3. I started doing this:
r= (.02m/(s^3))(5s^3)i + (2.2m/s)(5s)j - (.06m/(s^2)*(5s)^2k
r= 2.5mi + 11m + 1.5m
then I drew a 3d graph with each axis labeled and two right triangles but have no clue
where to go from here.
Phys.Org News Partner Science news on Phys.org
New model helps explain how provisions promote or reduce wildlife disease
Stress can make hard-working mongooses less likely to help in the future
Grammatical habits in written English reveal linguistic features of non-native speakers' languages
rl.bhat
#2
Sep14-10, 07:12 AM
HW Helper
P: 4,439
The given problem can be written as

r = a*t^3*i + b*t*j -c*t^2*k

Find d(r/dt and d^2(r)/dt^2. That gives you the acceleration. Find the magnitude of a.

Weight of helicopter is given. Find its mass. Then the force on the helicopter = m*a
dimeloom
#3
Sep14-10, 02:18 PM
P: 2
Thank you so mu rl.bhat.

After the 2nd derivative I get a= (.12m/s^3)(t) - .12m/s^2
= (.6m/s^2)- .12m/s^2= -.6 m/s^2
F=m*a m=F/a m=3000n/9.81m/s^2=305.8kg

m*a=F 305.8 kg * -.6m/s^2=-183.48N Is that thought process correct?

rl.bhat
#4
Sep14-10, 08:41 PM
HW Helper
P: 4,439
Find the net force with the given position vector

After the 2nd derivative I get a= (.12m/s^3)(t) - .12m/s^2

It should be

a= (.12m/s^3)(t)*i - .12m/s^2*k

Find the resultant a.


Register to reply

Related Discussions
How to determine Force from hor. position vector? Advanced Physics Homework 1
Coulombs law and vectors, find the force vector Introductory Physics Homework 4
Vector form of position, velocity, acceleration, and force Introductory Physics Homework 8
Find position vector from given velocity Introductory Physics Homework 5
Deriving Vector and position vectors from Force vector Introductory Physics Homework 3