(A) The boy has to overcome the force of gravity to climb the stairs.Force of gravity on the boy,$F = m \times g = 40 \, kg \times 9.8 \, m s^{-2} = 3

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Work = $1960 \, J$,Power = $392 \, W$

(A) The boy has to overcome the force of gravity to climb the stairs.Force of gravity on the boy,$F = m \times g = 40 \, kg \times 9.8 \, m s^{-2} = 392 \, N$.Total height (distance) covered,$S = 50 \times 10 \, cm = 500 \, cm = 5 \, m$.$(i)$ Work done by the boy in climbing,$W = F \times S = 392 \, N \times 5 \, m = 1960 \, J$.$(ii)$ Power developed,$P = \frac{W}{t} = \frac{1960 \, J}{5 \, s} = 392 \, W$.

Class 9 Science WORK AND ENERGY Mix Example - WORK AND ENERGY

Medium

$A$ boy of mass $40 \, kg$ runs up a flight of $50$ steps,each $10 \, cm$ high,in $5 \, s$. Find: $(i)$ the work done by the boy,and $(ii)$ the power developed. $(g = 9.8 \, m s^{-2})$

A
Work = $1960 \, J$,Power = $392 \, W$
B
Work = $1960 \, J$,Power = $3920 \, W$
C
Work = $196 \, J$,Power = $39.2 \, W$
D
Work = $19600 \, J$,Power = $3920 \, W$

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WORK AND ENERGY

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Mix Example - WORK AND ENERGY

State whether the following statement is true or false:
$A$ force does not work, if it produces no motion.

Easy

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Define work. Write an expression for work in terms of force and displacement. State the $SI$ unit of work done.

Easy

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What type of energy is stored in the spring of a watch?

Easy

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$(a)$ Define work done by a constant force on an object. Write an expression for the work done.
$(b)$ How much work will be done on an object by a force if the displacement of the object is zero?
$(c)$ What is the kinetic energy of an object? Write an expression for the kinetic energy of an object of mass $m$ moving with a speed $v$.

Medium

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In each of the following cases,a force $F$ is acting on an object of mass $m$. The direction of displacement is from west to east,shown by the longer arrow. Observe the diagrams carefully and state whether the work done by the force is negative $(-ve)$,positive $(+ve)$,or zero $(0)$.

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$A$ boy of mass $40 \, kg$ runs up a flight of $50$ steps,each $10 \, cm$ high,in $5 \, s$. Find: $(i)$ the work done by the boy,and $(ii)$ the power developed. $(g = 9.8 \, m s^{-2})$

Similar Questions

State whether the following statement is true or false:$A$ force does not work, if it produces no motion.

Define work. Write an expression for work in terms of force and displacement. State the $SI$ unit of work done.

What type of energy is stored in the spring of a watch?

In each of the following cases,a force $F$ is acting on an object of mass $m$. The direction of displacement is from west to east,shown by the longer arrow. Observe the diagrams carefully and state whether the work done by the force is negative $(-ve)$,positive $(+ve)$,or zero $(0)$.

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State whether the following statement is true or false:
$A$ force does not work, if it produces no motion.