Two men are each lifting straight over their heads an end of a 4.2 m plank with

Question

Two men are each lifting straight over their heads an end of a 4.2 m plank with mass 7.20 kg. a.) How much force does each man exert to hold the plank steady. b.) A 32 kg mass is placed 1.25 m from the left end. What is the force that each man exerts to hold the plank steady? c.) With the mass at the same location, the right man moves under the plank 0.75 m from his end and lifts while the left man remains lifting the board over his head from the end. How much force does each man now exert? I have the correct Answers; i need step by step solution a)Force from the left end=Force from the right end= 35.3 N b) Force from the right end = 129 N ; Force from the left= 256 N c) Force from the right= 157 N; Force from the left = 228 N Two men are each lifting straight over their heads an end of a 4.2 m plank with mass 7.20 kg. a.) How much force does each man exert to hold the plank steady. b.) A 32 kg mass is placed 1.25 m from the left end. What is the force that each man exerts to hold the plank steady? c.) With the mass at the same location, the right man moves under the plank 0.75 m from his end and lifts while the left man remains lifting the board over his head from the end. How much force does each man now exert? I have the correct Answers; i need step by step solution a)Force from the left end=Force from the right end= 35.3 N b) Force from the right end = 129 N ; Force from the left= 256 N c) Force from the right= 157 N; Force from the left = 228 N

Explanation / Answer

7.2 kg *9.81 m/s^2 = 70.63 N of for the board is exerting downard A) since the center of the mass of the board is equally spaced between the two men. the Reaction forces need by the two men are equal. therefore R1 and R2 = 70.63/2 = 35.31 N. B) The mass is now not uniformly distributed so you must use moments on each end to figure out the reaction forces 32kg*9.81 m/s^2 =313.92 N of force 1.25 m from the left end (R1) Now, with the moment around R1 M1 = 0 = -313.92 N*1.25m-70.63*2.1+R2*4.2 R2 (rightside) = 128.75 N Now the left side M2 = 0 = -70.63*2.1-313.92*(4.2-1.25)+R1*4.2 R1 (leftside)= 255.8 N C) Now the same thing just move the R2 to the left by .75 M1 = 0 = -313.92 N*1.25m-70.63*2.1+R2*(4.2-.75) R2 (right) = 156.73 N Moment around R2 is a little different now M2 = 0 = -70.63*(2.1-.75)-313.92*(4.2-1.25-.75)+R1*(4.2-.75) R1 (left) =227.82 N

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