Phys101
Term:122
Online HW-Ch14-Lec01
Q1:
The pressure exerted on the ground by a man is greatest when:
A.
B.
C.
D.
E.
he stands with both feet on the ground
he stands on one foot
he stands on the toes of one foot
he lies down on the ground
all of the above yield the same pressure
Ans:
C;
The weight of the man is the same in all case, so the pressure he
exerts on the ground will be largest if the area in contact with the
ground is the smallest. So C is the correct answer because the area of
the
toes
is
the
smallest
compared
to
the
other
mentioned
configurations.
Q2:
The diagram shows a U-tube with cross-sectional area A = 12.5×10-4
m2 and partially filled with oil of density 780 kg/m3. A solid
cylinder, which fits the tube tightly but can slide without friction, is
C
placed in the right arm. The system
is in equilibrium when L = 10
cm. Find the weight of the cylinder (in N).
(Give your answer in three significant figures
form)
Ans:
PD = PC
C
D
but PD ≡ pressure due to the weight of the cylinder
W
on area A: � � + P0 and PC = ρgL + P0
A
W
∴ + P0 = ρgL + P0 ⇒ W = ρgLA = 780 × 9.8 × 0.1 × 12.5 × 10−4
A
⇒ W = 0.956 N
KFUPM-Physics Department
1
Phys101
Term:122
Online HW-Ch14-Lec01
Q3:
Find the magnitude of the difference (in Pascal) in the pressure
exerted on an airplane at an altitude of 10 km above water level and
the pressure exerted on a diver 30 m below water level. Consider the
density of air to be 1.225 kg/m3, and that of water to be 1000 kg/m3.
(Give your answer in three significant figures form)
𝐀𝐧𝐬:
PD = ρ𝑙 gh + ρair gH + PA
⇒ |PD − PA | = ρ𝑙 gh + ρair gH = 1000 × 9.8 × 30 + 1.225 × 9.8 × 10 × 103
⇒ |PD − PA | = 414 × 103 Pa
KFUPM-Physics Department
2