Homework Help: What is the force exerted by a boulder on the bottom of a tank filled with water?

1. Oct 9, 2012

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

2. Oct 9, 2012

5ymmetrica1

I think this is what your looking for...

pressure = force/ area

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

3. Oct 9, 2012

Staff: Mentor

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

4. Oct 9, 2012

Staff: Mentor

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

5. Oct 9, 2012

kuhatelyn

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?

6. Oct 9, 2012

Staff: Mentor

Exactly.

Looks good to me.

7. Oct 9, 2012

kuhatelyn

Thank you!!!! :)