ELASTICITY & HYDROSTATIC

QUESTION 3th WEEK

QUESTION 1 ;

1. The height of the mercury column in barometer is 760 mm. Find the pressure of the atmosphere in pascals.

ANSWER 1 ;

1. p = pgh
= ( 13.6 X 10 ³ kg/ m³ ) ( 9.80 m/s ² )( 0.760 m)
= 1.013 X 10 ⁵ Pa.

QUESTION 2 ;

2. A metal ball weighs 0.096N. When suspended in water it has an apparent weight of 0.071N. Find the density of the metal.


ANSWER 2 ;

2. The desired density is given by p = m/V. But since the volume V of the ball is also the volume of displaced water, the buoyant force is given by B = p water g V. Thus,
p = (mg)p water / B
= (0.096 N)(1 X 10³ kg/m³ ) / ( 0.096-0.071) N
= 3840 kg/m³ .

QUESTION 3 ;

3. Air has a density of 1.29kg/m ³ under standard conditions. What is the mass of air in a room with dimensions
10m x 8m x 3m?


ANSWER 3 ;


3. m = p V
V = (10 m)(8 m)(3 m) = 240 m ³
m = (1.29 kg/m ³ )(240 m ³ )
= 310 kg.

QUESTION 4 ;

4. Approximately how large a force is required to stretch a 2.0 cm diameter steel rod by 0.01 percent?
Y= 195000 M Pa


ANSWER 4 ;

4. F = AY(∆ L/L )
= ∏(0.01)² (195 X 10⁹ ) (10 ⁻⁴)
= 6100 N


QUESTION 5 ;

5. A copper wire 2.0 m long and 2 mm in diameter is stretched 1 mm. What tension is needed? Young's modulus for copper is 117600 M Pa


ANSWER 5 ;

5. F/A = Y ( ∆ L/ L)
F = Y ( ∆ L/ L) A
= (117.6 X 10⁹ ) 0.001 / 2 ( ∏ ( 0.001 )² )
= 184.7 N.