Multiple choice

1. What is the minimum gauge pressure needed in the water pipe leading to a building if water is to come out of a faucet on the 12th floor, 41 m. above the pipe.
 
2. Estimate the pressure exerted on the floor by a 75 Kg. store clerk standing momentarily on a single heel of their shoe, where the heel area = 6.0 cm2 .

2a. What is pressure exerted in the first part expressed as “atmospheres” ?

3. A 30 Kg. balloon is filled with 100 m3 of helium. How much force is needed to hold it
down ?

4a. The lift used in an automotive garage consists of a pump exerting a constant pressure of 120 kpa. (kilopascal) on a hydraulic reservoir. The output piston connected to the lift has a diameter of 30.0 cm. What is the maximum force that can be exerted by this lift?

4b. A rectangular raft 3.0 m. long and 2.0 m. wide has a mass of 250 kg  What depth of fresh water is needed to float this raft?
  Weight of raft  = mg= 250kg( ) 9.81m/s2( ) = 2452.50N   
  Volume displaced by raft  = 3.0m( ) 2.0m( ) depth( ) = 6m2 *depth  
Bouyant force from displaced water = ρ freshwatergV
Bouyant force from displaced water = 1000 kg/ m3( ) 9.81m/ s2( ) 6 m2 * depth( )
Bouyant force from displaced water = 58, 860 N / m( )* depth( )
Since the buoyant force must balance the weight of the raft in order for it to float,  we can write:  

4c. A DC-10 aircraft is flying at an altitude where the atmospheric pressure is 40% of sea level pressure. If the aircraft interior is maintained at sea level pressure, what is the size and direction of the net force acting on a cabin door that is 1.0 meters wide and 2.0 meters high ?

5. The Hydraulic press is able to produce a mechanical advantage because: 
a) the force a fluid exerts on a piston is always parallel to its surface
b) an external pressure exerted on a fluid is transmitted uniformly throughout its volume
c) at any depth in a fluid the pressure is the same in all directions
d) the pressure in a fluid varies with its speed 
 
6. In the operation of a hydraulic press, it is impossible for the output piston to exceed the input piston’s:
a) displacement
b) speed
c) force
d) work
 
7. Fluid at rest at the bottom of a container is:
a) under less pressure than the fluid at the top
b) under the same pressure as the fluid at the top
c) under more pressure than the fluid at the top
d) any of the above, depending on the circumstances

8. The pressure at the bottom of a vessel filled with liquid does not depend on :
a) the acceleration of gravity
b) the liquid density
c) the height of the liquid
d) the area of the liquid surface
 
9. In order for an object to sink when placed in water, its average specific gravity (relative density) must be:
a) less than 1
b) equal to 1
c) more than 1
d) any of the above, depending on its shape
 
10. A cake of soap placed in a bathtub of water sinks. The buoyant force on the soap is:
a) zero
b) less than its weight
c) equal to its weight
d) more than its weight
 
11. The density of fresh water is 1.00 gm/cm3 and that of seawater is 1.03 gm/cm3 A ship will float:
a) higher in fresh water than in seawater
b) at the same level in fresh water and in seawater
c) lower in fresh water than in seawater
d) any of the above, depending upon the shape of the hull

12. An express train on the subway goes past a station platform at high speed. A person
a) standing at the edge of the platform tends to be :
b) attracted to the train
c) repelled from the train
d) attracted or repelled, depending on the ratio between the speed of the train and the speed of sound
unaffected by the train’s passage
 
13. The input piston of a hydraulic press is 20 mm in diameter, and the output piston is 10 mm in diameter. An input force of 1.0 N will produce an output force of :
a) 0.25 N
b) 0.50 N
c) 2.0 N
d) 4.0 N
 
   14. A manometer whose upper end is evacuated and sealed can be used to measure atmospheric pressure. Such an instrument is called a mercury barometer, and the average height of the mercury column in it is 760 mm. If water were used in the barometer instead of mercury, the height of the column of water would be about :
a) 56 mm
b) 760 mm
c) 10 m
d) 20 m
 
15. Airplane travelers often note that their cosmetics bottles and other containers have leaked after a trip. What might cause this?
 
16. An ice cube floats in a glass of water filled to the brim. As the ice melts, will the glass overflow?
 
17. A barge filled high with sand approaches a low bridge over the river and cannot quite pass under it. Should sand be added to, or removed from, the barge?
 
18. Will a helium filled balloon rise indefinitely in the air? Explain
 
  19. Why does the stream of water from a faucet become narrower as it falls?