Question

W weight lifter lifts a 150 kg barbell above his head from the floor to a height of 2 m, He holds the barbell there for 5 seconds. How much work does he do during that 5 sec interval?

Answer 1

Given:-

• Mass of ball ,m = 150 kg

• Height ,h = 2m

• Time ,t = 5 s

To Find:-

• Work done ,W

Solution:-

As we know that the acceleration due to gravity is 9.8m/s² on the earth's surface.

Firstly we calculate the Force

• F = m×g

Substitute the value we get

→ F = 150 × 9.8

→ F = 1470 N

Therefore, the force acting on man is 1470 Newton

Now Calculating the Work Done.

• W = F×s

Here,

F is the Force

s is the displacement

W is the Work Done

Since the displacement of man is 0

Therefore, the work done

Substitute the value we get

→ W = 1470×0

→ W = 0 J

Therefore, the work done by the man is 0 Joule.

Answer 2

Solution

Given,

• the height =2m
• the mass = 150 kg
• Time taken = 5sec

To find,

• work done by him ?

note :- the displacement of man is zero .

first of all we have to calculate here the force ;

We know that ,

$= > \red{f = mg}$

now putting the value we get ,

$\green{= > 150 \times 9.8} \\ \green{= > 1470}$

now to find the work done by him ,

We know that ,

$= > \red{w = fs}$

now putting the value we get ,

$= > \green{1470 \times 0}$

$\green{ = > 0j }$

The work done is 0 joules .