Question

A boy mass 40 kg runs upstairs and reaches the first floor which is 8m high in 5s. Calculate.
(1)The force of gravity acting on the boy.
(2)The work done by him against gravity.

Answer 1

Given:-

• Mass of boy (m) = 40kg

• Height (h) = 8m.

• Time Taken (t) = 5s.

To Find:-

• Force of gravity (F) and Work done by him against gravity (W).

Solution:-

(1)

As we know that Force is the product of mass and acceleration .

We know that the acceleration due to gravity is 9.8m/s²

By using this formula

⟹ Force = Mass × acceleration ( acceleration due to gravity)

⟹ F = Mg

Substituting the value ,we get

⟹ F = 40×9.8

⟹ F = 394N.

∴ The force of gravity acting on the body is 394N.

(2)

By using this formula

⟹ Work done = Mass× Acceleration × Displacement

⟹. W = mgh

Substituting the value we get

⟹ W = 40×9.8×8

⟹ W = 392×8

⟹ W = 3136 J

∴The work done by him against gravity is 3136Joules

Answer 2

$\tt\huge{\green{Answer}}$

$\tt \large{\red{Given}}$

• mass(m)= 40kg
• Height (h) = 8m
• Time taken (t)= 5s

$\tt\large{\red{To \: find :-}}$

• The force of gravity acting on boy
• The work done by him against gravity

$\textbf{\large{\red{Solution :-}} }$

1 :-

$\dashrightarrow$As we know that force is a product of mass (m) and acceleration(a).

$\dashrightarrow$ we know tha acceleration due to gravity is 9.8m/s.

so,

By using this formula .

$\: force \: = mass \: \times \: acceleration \: .$

( acceleration due to gravity )

$\dashrightarrow$ F = mg.

so ,

$\dashrightarrow$F = $40 \: \times \: 9.8 \: = \: 394 \: n \:$

$\tt\</strong><strong>l</strong><strong>a</strong><strong>r</strong><strong>g</strong><strong>e</strong><strong>{\red{</strong><strong>H</strong><strong>e</strong><strong>n</strong><strong>c</strong><strong>e</strong><strong> </strong><strong>,</strong><strong> </strong><strong>}}$

$\dashrightarrow$ F = 394 N .

So,

The force of gravity acting on body is 394 N.

By using this formula .

$\dashrightarrow$ Work done = Mass * acceleration * Displacement .

$\dashrightarrow$ W = mgh.

Putting the value we get .

$\dashrightarrow$ W = 40 * 9.8 * 8 .

$\dashrightarrow$W = 392 * 8

$\dashrightarrow$ W =3136 J ( joule)

:- The work done by boy agains gravity is 3136 J ( joule )