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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