A ladder AB is supported by a smooth vertical wall and rough horizontal floor as shown. A boy starts moving from A to B slowly. The ladder remains at rest, then pick up the correct statement(s):
A
Magnitude of normal reaction by wall on ladder at point B will increase.
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B
Magnitude of normal reaction by wall on ladder at point B will decrease.
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C
Magnitude of normal reaction by floor on ladder at point A will remain unchanged.
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D
Magnitude of frictional force by the floor on ladder at point A will increase.
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Solution
The correct options are A Magnitude of normal reaction by wall on ladder at point B will increase. C Magnitude of normal reaction by floor on ladder at point A will remain unchanged. D Magnitude of frictional force by the floor on ladder at point A will increase.
Let m and M be mass of man and ladder. From FBD normal reaction at A is N1=(m+M)g which remains constant. Net torque on man + ladder is zero about B. If x decreases then torque of mg about B will decrease. Hence f must increase.