(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

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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Water stored in a dam possesses

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$A$ weightlifter lifts $240 \,kg$ from the ground to a height of $2.5 \,m$ in $3 \,s$. The average power is:

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Compare the power at which each of the following is moving upwards against the force of gravity? (given $g = 10 \, m \, s^{-2}$)
$(i)$ $A$ butterfly of mass $1.0 \, g$ that flies upward at a rate of $0.5 \, m \, s^{-1}$.
$(ii)$ $A$ $250 \, g$ squirrel climbing up on a tree at a rate of $0.5 \, m \, s^{-1}$.

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The velocity of a body moving in a straight line is increased by applying a constant force $F$, for some distance in the direction of the motion. Prove that the increase in the kinetic energy of the body is equal to the work done by the force on the body.

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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

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 $(0)$.

Water stored in a dam possesses

$A$ weightlifter lifts $240 \,kg$ from the ground to a height of $2.5 \,m$ in $3 \,s$. The average power is:

The velocity of a body moving in a straight line is increased by applying a constant force $F$, for some distance in the direction of the motion. Prove that the increase in the kinetic energy of the body is equal to the work done by the force on the body.

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