Register to reply 
Backpack on a line 
Share this thread: 
#1
Oct2508, 07:45 PM

P: 114

1. The problem statement, all variables and given/known data
The two trees in the figure are 6.9m apart. A backpacker is trying to lift his pack out of the reach of bears. (a)Calculate the magnitude of the force F that he must exert downward to hold a 15 kg backpack so that the rope sags at its midpoint by 1.5m . (b)Calculate the magnitude of the force that he must exert downward to hold a 15 kg backpack so that the rope sags at its midpoint by 0.16m . 2. Relevant equations 3. The attempt at a solution Distance between the trees =6.6 m Half of distance between the trees = b =6.9/2= 3.45 m sag at mid point = a = 1.5 m Consider the vertical right anglled triangle with ' b ' as base, ' a ' as height and the half portion of rope as hypotenues ' h ' The hypotenues = h = sq rt [ b^2 + a^2 ] , h = sq rt [ 3.45^2 +1.5^2 ] h =3.762 m Now the hypotenues ( h = 3.762 m ) represents force Fand side 'a' represents weight 98 N F/h =(15kg*9.8)/a F /3.762 =147 /1.5 m F =368.7 N This is answer is not right. I dont know what im doing wrong :S Please guide me 


#2
Oct2508, 08:40 PM

Mentor
P: 21,215

[QUOTE=itryphysics;1929899] Now the hypotenues ( h = 3.762 m ) represents force Fand side 'a' represents weight 98 N [quote] The weight is wrong. The mass of the pack is 15 kg, so its weight is 15 * 9.8 = 147 N. Your later work seems to use the right value. You said you didn't think this was correct. What's the answer you believe is correct? 


Register to reply 
Related Discussions  
Line that intersects and is perpendicular to another line  Calculus & Beyond Homework  1  
Find the equation of the normal line of the given parabola that is parallel to a line  Calculus & Beyond Homework  9  
Equation of line parallel to plane and intersaction with other line  Precalculus Mathematics Homework  5  
Asteroid Collision Course and Sagging Backpack  Introductory Physics Homework  6  
Bicycle Jet Backpack  General Discussion  7 