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Answer:
C
Explanation:
To melt the alcohol
Heat needed = M . L = 2 . 25 = 50 kcal
To warm up the alcohol
Heat needed = M . sp. ht. . ∆t = 2 . 0.6 . 100 = 120 kcal
Total heat needed = 170 kcal
Assuming that 0.6 kcal/ kg / ˚C is the specific heat and that the answer is wanted in kcal ( a rather odd unit to be in use here.)
The work done to pull the sister back on the swing is equal to the increase in potential energy of the sister:

(1)
where m is the sister's mass, g is the gravitational acceleration and

is the increase in altitude of the sister with respect to its initial position.
By calling

the angle of the chain with respect to the vertical, the increase in altitude is given by

(2)
where L is the length of the chain.
Putting (2) inside (1), we find

from which we can find the mass of the sister:
Answer:
the 70kg man
Explanation:
because he has more weight and is moving faster