Question

A man of mass 70kg carries a stone of mass 20kg to the top of a buliding of height60m. calculate the total workdone spent by him

Answer 1

GiveN :

• Mass of man (m_1) = 70 kg
• Mass of stone (m_2) = 20 kg
• Height of building (h) = 60 m

To FinD :

• Work done by man

SolutioN :

⇒Total Mass = Mass of Stone + Mass of Man

⇒ Total mass = 70 + 20 = 90 kg

As we know by work energy theorem that :

$\dashrightarrow \boxed{\tt{W \: = \: mgh}} \\ \\ \dashrightarrow \tt{W \: = \: 90 \: \times \: 10 \: \times \: 60} \\ \\ \dashrightarrow \tt{W \: = \: 900 \: \times \: 60} \\ \\ \dashrightarrow \tt{W \: = \: 54000J} \\ \\ \dashrightarrow \tt{W \: = \: 54 \: kJ} \\ \\ \underline{\sf{\therefore \: Work \: Done \: by \: man \: is \: 54 \: kJ}}$

Answer 2

Solution :

✴ Given :-

• Mass of man = 70kg
• Mass of stone = 20kg
• Height of building = 60m
• Total mass = 70+20 = 90kg

✴ To Find :-

• Work done by man to carry stone from ground to the height

✴ Concept :-

▪ This question is completely based on concept of 'Work-Energy theorem'

▪ As per WET, work done by body is always equals to the change of energy.

✴ Calculation :-

$\implies\sf\:\red{Work=\triangle{Potential \: Energy}}\\ \\ \implies\sf\:W = Mg\triangle{H}\\ \\ \implies\sf\:W=90\times 10 \times (60-0)\\ \\ \implies\sf\:W=900\times 60\\ \\ \implies\:\boxed{\sf{\pink{\large{Work \:done=54 kJ}}}}$

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• Work and Energy both are scalar quantity.
• Potential energy is a relative quantity in other work it requires reference point to define.