A Uniform beam PQ of mass 20kg and length 5m is balanced as shown above, a man of weight 800N stands at M such that QM = 2m. The reaction at P and Q respectively are(take g = 10ms-2)
300N and 500N
420N and 580N
220N and 380N
580N and 420N
382N and 220N
Explanation
Video Explanation
No video available
Post your Contribution
Discussions (12)
B correct
From the law of equilibrium, total downward force is equal to total upward force.
Downward forces are weight of man(800N) and weight of beam(20×10=200N)
Total upward forces are P and Q
So P+Q=800+200=1000N.
The beam is uniform so weight acts at the center, distance 2.5m
From condition of equilibrium, total clockwise moments = total anticlockwise moment.
Taking moments at Q
(200×2.5)+(800×2)=( P×5)
500+1600=5P
5P=2100
Reaction at P=2100/5
P=420N
Remember P+Q=1000
420+Q=1000
Q=1000-420
Q=580N
Reaction at P and Q are respectively 420N and 580N
