5.4 Harder questions on Pressure
07 October 2011
16:30
· Collins, p.107, Q.4.
Question 4
Answer
Ordinary shoe=
P = F/A = 400 / ( 0.05 X 0.05) = 160000 N/m2 or 160K Pa
Elephant
P= F/A= 5000/(pie X 0.1^2) = 159,000N/m2 or 159KPa
High heels
P= F/A = 400/0.0005=8,000,000 N/m2
Wooden Floor = 4000KPa = 4,000,000 N/m2
The high heel will damage the floor.
5.4 recall and use the relationship between pressure, force and area:
pressure = force / area
p = F / A
Collins p.106 Q.1-3. (Table of densities below)
Q1.
o Wood in oil = depend on the wood
o Wood in mercury = Wood will float
o Plastic in oil = Plastic will sink
o Steel in mercury = Steel will float
o Silver in air = Air will sink
o Gold in mercury = Gold will sink
o Helium balloon in air = Air will sink
Q2.
Volume = 0.2 X 0.09 X 0.065 = 0.0017
Mass = 22.2/10 = 2.22
Density = Mass/ Volume
= 2.22/0.00117 = 1897kg/m3
Q3. 900 cm3
Density of an irregular solid
Method
Measure mass using balance
Measure volume by using the displacement method (submerge solid in a Eureka can and collect the overflow in a measuring cylinder
Calculate density (D=m/V)
M=123.3 g
V= 43.20 cm3
D=M/V
D=123.3/43.2
=2.854 g/cm3
How can you make a cannonball float?
Explanation below…
Density of Iron = 7.9g/cm3 or 7,900kg/m3
Density of Mercury = 13.6g/cm3 or 13,600kg/m3
5.2 recall and use the relationship between density, mass and volume:
density = mass / volume
ρ = m / V
Mass= 567.5g
Width=5cm Length=5cm Height=2cm
V=wlh = 5x5x2= 50cm3
Density = m/v = 567.5/50= 11.4 g/cm3
