HW 7

You live in an apartment directly above an open-air tavern and you possess a really, really long and sturdy straw. You plan to steal beer by leaning out of your apartment window and, when the beer-drinkers are not looking, sticking your straw into beer glasses and sucking on the straw. Assuming you can create a perfect vacuum when you suck on the straw, for this plan to have a chance of working, the height difference between you and the beer must be less than approximately what distance? (Assume the density of beer is equal to the density of water and the pressure is 1 atm = 101 kPa.)

10 m

A 500 N weight sits on the small piston of a hydraulic machine in equilibrium. The small piston has area 2.0 cm2. If the large piston has area 40 cm2, how much weight does the large piston support?

10000 N

Let g = 9.8 m/s2. A hydraulic system is used to lift a 66 kg motor in a garage. If the motor sits on a piston of area 0.36 m2, and a force is applied to a piston of area 63 cm2, what is the minimum force that must be applied to lift the motor in units of N? Enter a number with one digit behind the decimal point.

11.3

A 13 kg object is placed on a 106 cm2 platform. What is the pressure the object exerts on the platform in N/m2? Let g = 9.8 m/s2. Enter an integer.

12019

A 2 kg block of wood is floating in water. What is the magnitude of the buoyant force acting on the block?

19.6 N

A 26 kg object is placed on a 114 cm2 platform. What is the pressure the object exerts on the platform in N/m2? Let g = 9.8 m/s2. Enter an integer.

22351

Substance A has a density of 3.0 g/cm3 and substance B has a density of 4.0 g/cm3. In order to obtain equal masses of these two substances, the ratio VA/VB of the volume of A to the volume of B has to be equal to

4 : 3

Mercury has an unusually large surface tension γ = 0.465 N/m. Calculate the excess pressure inside a drop of mercury 4 mm in diameter.

465 Pa

A 50 kg woman balances on one heel of a high-heel shoe. If the heel is circular with radius 0.5 cm, what pressure does she exert on the floor?

6.2 MPa

You are bored during the summertime when school is not in session and you decide to do an experiment where you compare the properties of water and air. If the density of air is 1.25 kg/m3 and the density of water is 1000 kg/m3, what volume of air weighs the same as 1 liter (10-3 m3) of water?

800 liters

The vessels shown below all contain water to the same height.Rank them according to the pressure exerted by the water on the vessel bottoms, least to greatest.

All pressures are the same.

The picture below shows 5 blocks. The blocks have equal volumes but different masses. The blocks are placed in an aquarium tank filled with water and blocks 2 and 5 come to rest as shown in the figure. Which answer is correct?

Block 3 will come to rest in the same position as block 5.

In a stationary homogeneous liquid near the surface of Earth, which of the following is true?

Pressure is the same at all points at the same height.

The shape of a droplet of liquid on a surface is due to a combination of

adhesion and cohesion

A boat is floating in a lake. Since it is floating the buoyant force acting on the boat must be

equal to its weight.

Suppose you have two containers with liquid in them. One has a density of 760 kg/m3 and the other has a density of 910 kg /m3. If an object floats in one container and sinks in the other, the density of the object

has a value between 760 kg/m3 and 910 kg/m3

One kilogram of iron (density ~7.8 gm/cm3) and 1 kilogram of aluminum (density ~2.7 gm/cm3) are dropped into a pool. Which is acted on by the largest buoyant force?

the aluminum

A beaker is filled with water to the rim. Gently you place a toy duck in the beaker and some of the water spills out. The duck floats. The weight of the beaker with the duck floating in it is

the same as its weight before adding the duck.

Suppose you have an aquarium. You have a solid plastic decoration and a rock of about the same volume but the rock has twice the mass. Both are totally submerged in the water. The buoyant force on the plastic object is about

the same as that on the rock.