ICSE Class 10 Answered

Fig.1 shows the metal rod of mass M = 120 g and length 80 cm is supported at a point 35 cm from left end A.

Since the metal rod is supported at 35 cm from left end A, center of mass of metal rod is at this point of support.

Hence center of mass of metal rod is  (80-35) cm = 45 cm from right end B .

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Fig.2 shows that the point of support of metl rod is at 30 cm from left end A .

Since weight of the metal rod is acting at center of mass which is right side of point of support ,

we need to hang another mass m at left side of support point .

Let the distance of mass m from support point is x as shown in fig. 2 .

If we take moment of forces with respect to support point , then we get

where M = 120 g  and m = 40 g

Hence we get ,  40 x = 120 × 5  

from above expression we get x = 15

Hence 40g mass has to be hanged at a distance 15 cm from left end A of metal rod.