Physics Help Forum Pulley/Cable Problem

 Kinematics and Dynamics Kinematics and Dynamics Physics Help Forum

 Apr 21st 2009, 04:19 AM #1 Junior Member   Join Date: Apr 2009 Posts: 2 Pulley/Cable Problem Can someone show a step by step solution of this problem? Thanks! The pulley/cable system shown in the attachment is connected to a mass, m, which is accelerating downward at an acceleration of 8 ft/s2, despite the force in the cable, F = 100 lbs. What is the mass, m, of the object? a = 8 ft/s2 F = 100 lbs m = ? Attached Thumbnails
 Apr 22nd 2009, 03:49 AM #2 Physics Team   Join Date: Feb 2009 Posts: 1,425 As usual cant open your thumbnail so working blind. Accln due to gravity is 32 ft/sec^2. Since it is lower here obviously the force opposes the grav force. The net force on the mass is therefore f given by f = m x 8 = m x 32 - 100 . Solving, m = 4.166 lbs.
 Apr 22nd 2009, 10:20 AM #3 Physics Team   Join Date: Feb 2009 Location: India Posts: 365 Since force F is applied to the cable, the tention through out the cable will be F (assumong cable and pulleys massless). Now the force upward due to cable will be 6F( six cables support the mass) and force down ward is mg. Since the mass is accellerating down ward hence net force on it(mg - 6F) will be down ward. Using Newton's second law, we get mg - 6F = ma. Put the values of g and a ( = 8 ft/s^2) and find m.

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