TPR Physics Question

[Perseverance7779311]

Hi guys, the question reads,
A 10 kg rock, with volume 0.001m^3, sits at the bottom of a pool filled with water. Find the force exerted on the rock by the bottom surface of the pool.

The first part of the answer reads:
FN + FB -mg=0

Could someone please tell me why ma is equal to 0? Thank you.

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[Cawolf]

The rock isn't moving so a = 0.

 

[Perseverance7779311]

@Cawolf, so would it be true that whenever an object is not moving, a will always be equal to 0?

 

[Cawolf]

Yes.

v = at

if v = 0 (not moving) then 0 = at and a = 0.

That fact should be rather intuitive though. If acceleration is the change in velocity per unit time, then how can something that is not moving have any acceleration?

The converse is not true though;

an object that is moving may still have a = 0 if velocity is constant.

 

[DoctorInASaree]

@Cawolf, so would it be true that whenever an object is not moving, a will always be equal to 0?

No v no a!

@Cawolf Darn, the wolf is quick!

 

[Perseverance7779311]

@Cawolf, thank you!

 

[Cawolf]

Sorry Saree.

I am sitting in the library atrium just browsing forums and listening to Audio Osmosis. So I was ready for it!

 

[Perseverance7779311]

@DoctorInASaree , thank you!