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itryphysics
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Homework Statement
The two trees in the figure are 6.9m apart. A back-packer 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 .
Homework Equations
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 don't know what I am doing wrong :S Please guide me