Question

Examples for positive, zero and negative work

Answer 1

Here is a list of some examples of work done.

Work done is divided into:

a) Positive Work done and b) Negative Work done

a)Examples of positive work done

1. Kicking a football

2. Moving a chair

3. Throwing a stone

4. Riding a bicycle

5. Doctors moving a patient in wheel chair

6. striking a pen into another pen

7. Riding a skateboard

8. Pushing and moving a table

9. Cutting a fruit with knife

10. A car moving forward

b)Examples of Negative Work done

1. Someone pushes you when you are trying to be at your position

2. You are pulled from behind when you try to move the front

3. In Arm wrestling, when someone is defeating you.

4. In Tug of War when the opponent team pulls hard.

5. Pushing a car up a hill, when you slip back.

6. Trying to catch a heavy object, hands move down

7. When you jump, work done by gravity is negative

8. After you press a spring, it relaxes.

9. Trying to kick a moving football, work done by the ball is negative

10. A car moving on the road, work done by friction is negative

zero work

Take a box. Lift it straight up & move forward. Though you will get tired, but according to physics, you have done no work.

Since WORK=FORCE. DISPLACEMENT in the direction of force

$workdone=F\times d\times \cos \theta$

Where $\theta$ is the angle between force & displacement.

Here $\theta$ will 90 therefore $\cos \theta$ will be 0. Therefore work is 0.
$\cos \theta$ is negative work done will be negative
$\cos \theta$ is positive work done will be positive