Force Exerted by 20,000N Boulder in 0.4m^3 Tank

[kuhatelyn]

I know the weight of the boulder is 20,000 N and the volume is 0.4 m^3
Wouldn't the answer just be 20,000? Since the force is the same thing as weight?
the options are:

(a) 12,460
(b) 17,860
(c) 16,080
(d) 14,450
(e) none of these

 

[5ymmetrica1]

I think this is what your looking for...

pressure = force/ area

p = 20000/0.4
= 50000 N/m^2

 

[NascentOxygen]

I know the weight of the boulder is 20,000 N and the volume is 0.4 m^3
Wouldn't the answer just be 20,000? Since the force is the same thing as weight?
the options are:

(a) 12,460
(b) 17,860
(c) 16,080
(d) 14,450
(e) none of these

Weight is a force of attraction due to gravity, yes.
Do you know a value for the density of water?

 

[Doc Al]

Wouldn't the answer just be 20,000? Since the force is the same thing as weight?

No. What effect does surrounding the boulder with water have?

 

[kuhatelyn]

No. What effect does surrounding the boulder with water have?

Oohhh, so I would calculate the buoyant force and then subtract that from the weight of the boulder, so I get the force that the boulder exerts on the ground?

If I multiply volume x density of water x force of gravity:
0.4 x 1000 x 9.8 = 3920
and then subtract this from 20,000 I get 16080.
Is that right?

 

[Doc Al]

Oohhh, so I would calculate the buoyant force and then subtract that from the weight of the boulder, so I get the force that the boulder exerts on the ground?

Exactly.

If I multiply volume x density of water x force of gravity:
0.4 x 1000 x 9.8 = 3920
and then subtract this from 20,000 I get 16080.
Is that right?

Looks good to me.

 

[kuhatelyn]

Thank you! :)