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suvat question

if an object is released from rest and hit the ground, why isn't both initial and final velocity 0?
but that logic doesn't seem to work in my prep
Original post by alvan15
if an object is released from rest and hit the ground, why isn't both initial and final velocity 0?
but that logic doesn't seem to work in my prep


The SUVAT equations are derived for a point mass undergoing a constant acceleration.

If an object hits the ground at a non-zero velocity, it is subject to an force in the direction opposite to its velocity i.e. there is a non-constant acceleration.
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alvan15
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Original post by pleasedtobeatyou
The SUVAT equations are derived for a point mass undergoing a constant acceleration.

If an object hits the ground at a non-zero velocity, it is subject to an force in the direction opposite to its velocity i.e. there is a non-constant acceleration.


so are you suggesting that either initial or final velocity has to be 0?
Original post by alvan15
so are you suggesting that either initial or final velocity has to be 0?


objects with mass can't stop instantly, typically it'll hit the floor and start to compress. Could be a very rapid deceleration but not instant.

this type of question is usually asking about the instant the falling object contacts the floor, which is it's greatest velocity.

have to be quite general cos you haven't posted the question you're having trouble with.
Original post by alvan15
so are you suggesting that either initial or final velocity has to be 0?


No, I didn't suggest that, it was you who stated it originally - although it is the case.

I'm stating that the SUVAT equations are not valid for the problem you described since the impact of a point mass with a solid, immovable surface does not constitute an event where the acceleration of the system is constant.

The acceleration is not constant for all time and for this scenario, the acceleration can be modeled with the concept of impulse, which you may or may not have covered yet.
(edited 7 years ago)
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alvan15
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Original post by pleasedtobeatyou
No, I didn't suggest that, it was you who stated it originally - although it is the case.

I'm stating that the SUVAT equations are not valid for the problem you described since the impact of a point mass with a solid, immovable surface does not constitute an event where the acceleration of the system is constant.

The acceleration is not constant for all time and for this scenario, the acceleration can be modeled with the concept of impulse, which you may or may not have covered yet.


yes i have, thank you, i get it now :smile:

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