Physics Questions

Seashore

2009-04-10 9:33 pm

1. A bicyclist is traveling at a speed of 20.0 m/s as he approaches the bottom of a hill. He decides to coast up the hill and stops upon reaching the top. Neglecting friction, determine the vertical height of the hill.

a) 28.5 m

b) 3.70 m

c) 11.2 m

d) 20.4 m

e) 40.8 m

2. A woman is enjoying a tropical drink while lying on a beach. The acceleration due to gravity at her location is 9.85 m/s2. What gauge pressure must exist in the woman's mouth if she is drinking through a straw extending 0.085 m above the surface of the drink? Note: Assume the drink has a density of 1015 kg/m3.

a) 970 Pa

b) 1100 Pa

c) 2100 Pa

d) 850 Pa

e) 1.0 × 105 Pa

回答 (1)

老爺子

2009-04-10 10:57 pm

✔ 最佳答案

1.
The answer is d.

Initial K.E. of the bicycle = P.E. gain when reaching the top of hill
(1/2)mv2 = mgh
(1/2)m(20)2 = m(9.8)h
Vertical height of the hill, h = 20.4 m

2.
The answer is d.

Let the cross-sectional area of the straw be A m3.
Volume of the drink in the straw, v = area x height = 0.085A m3
Density of the drink, ρ = 1015 kg/m3
Mass of the drink in the straw, m= vρ = 0.085A x 1015 = 86.3A kg
Weight of the drink in the straw, W = mg = 86.3A x 9.85 = 850A N
Pressure, P = W/A = 850A/A = 850 Pa
=

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