Question Number 31111 by Tinkutara last updated on 02/Mar/18
Commented by Tinkutara last updated on 02/Mar/18
Answered by rahul@ last updated on 02/Mar/18
Commented by Tinkutara last updated on 02/Mar/18
but why cases first and second aren't identical?
Commented by momo last updated on 02/Mar/18
$${why}\:{identical}??? \\ $$
Commented by mrW2 last updated on 03/Mar/18
Why the both cases are not identical:
To keep a still object in its position you only need to fight against the gravity (static force).
To stop the same object at the same position but in motion (i.e. with a speed) you must not only fight against the same gravity, you also need to rapidly reduce its speed, i.e. to give it a big negative acceleration, and acceleration means addtional force (dynamic or impact force). Therefore to stop a moving object, you need to apply a much bigger force than just to keep it in still position.
Since a=v/t, we can say, the shorter the time in which you stop the moving object, the bigger the force you need to apply.
Commented by mrW2 last updated on 03/Mar/18
So it is relatively easy to prevent a car to move on a slope. But it is very hard to hold it back if it is already in motion.
Commented by Tinkutara last updated on 03/Mar/18
�� Thanks mrW2 and rahul@ Sir.