Question

Suppose you are running and want to stop at once. Surely you will have to produce negative acceleration in your speed. Can you tell from where does the necessary force come?
plz answer...​

Answer 1

To discuss:

Suppose you are running and want to stop at once. Surely you will have to produce negative acceleration in your speed.

From where does that negative acceleration (retardation) come from ?

Solution:

Lets assume that you are running at a initial velocity of "u" , and then you need to stop, hence you apply an acceleration of "-a" (i.e. retardation).

So, the distance taken to stop will be v²/2a

But the question arises , from where does that force arise ??

• Let me try to explain it in the easiest way possible.

• First of all, when we think of stopping at a certain point while running, our brain sends a ELECTRICAL SIGNAL to the muscles of the foot and leg.

• The body is positioned in such a way, that the normal reaction between the foot and the road increases.

• This increases the frictional force between the foot and the road.

• Hence, a greater retardation (negative acceleration) will be experienced by the runner, such that he/she will stop in the specified distance (as calculated earlier).

• Also while stopping, the runner makes his/her body more straight, which results in more air resistance. This also adds to the retardation.

$\star$ Hope It Helps.

Answer 2

To discuss:

Suppose you are running and want to stop at once. Surely you will have to produce negative acceleration in your speed.

From where does that negative acceleration (retardation) come from ?

Solution:

Lets assume that you are running at a initial velocity of "u" , and then you need to stop, hence you apply an acceleration of "-a" (i.e. retardation).

So, the distance taken to stop will be v²/2a

But the question arises , from where does that force arise ??

• Let me try to explain it in the easiest way possible.
• First of all, when we think of stopping at a certain point while running, our brain sends a ELECTRICAL SIGNAL to the muscles of the foot and leg.
• The body is positioned in such a way, that the normal reaction between the foot and the road increases.
• This increases the frictional force between the foot and the road.
• Hence, a greater retardation (negative acceleration) will be experienced by the runner, such that he/she will stop in the specified distance (as calculated earlier).
• Also while stopping, the runner makes his/her body more straight, which results in more air resistance. This also adds to the retardation.