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Find the net force with the given position vector 
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#1
Sep1310, 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. 


#2
Sep1410, 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 


#3
Sep1410, 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? 


#4
Sep1410, 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. 


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