A uniform wooden plank 68cm long and weighing 38N rest horizontaly on two knife edges each 10cm from the ends of the plank. (1) What is the greatest land which applied at one end of the plank will not cause it to over turn. (2) what are the reactions of the support cohese a weight of 5N is supported at one end and another weight of 25N supported at the middle.

Question

A uniform wooden plank 68cm long and weighing 38N rest horizontaly on two knife edges each 10cm from the ends of the plank.                                                                  (1) What is the greatest land which applied at one end of the plank will not cause it to over turn.                                       (2) what are the reactions of the support cohese a weight of 5N is supported at one end and another weight of 25N supported at the middle.

plato · Accepted Answer

for balance:clockwise moment=anticlockwise moment:using one edge of knife as reference: L*10=38*24 L=91.2N (2)R1+R2=38+25+5=68N using one support:clockwise movement=48R1+5*10 anticlockwise moment=(25+38)*24 clockwise moment equals anticlockwise moment:48R1+50=1512 R1=33.6N R2=68-33.6 R2=34.4N