Second term PHYSICS class test 1 OF class 9 ( 2022-23)

 1. Why  one cannot suck lemonade on the surface of moon with soda straw?

Ans. On the surface of Earth, when suρction is caused on the end of the soda straw, the pressure falls within it. Thus, atmospheric pressure forces the lemonade up the straw. But on the surface of moon there is no atmospheric pressure. so lemonade cannot be pushed up the straw.

2.calculate the pressure exerted by 75 cm of vertical length of water column in SI and CGS units.

Ans. Vertical length of water column (h)= 75cm

                                          = 75/100 m = 0.75m

Density of water = 1000 kgm‐³

Acceleration due to gravity= 9.8 ms-²

Pressure = h×ρ×g

P= 0.75m × 1000 kgm-³ × 9.8ms-²

   = 7350 kgms-² /m²

= 7.350 × 10³ pa

Ine cgs unit

    Pressure=ρ× h×g

        = 75 cm × 1.0 gcm-³ × 980 cms-²

        = 73500gcms-² / cm²

         = 73500 dyne cm-²

         = 7.35 × 10⁴ dyne/cm²

3. Calculate the equivalent height of a water barometer, if the pressure recorded by mercury barometer is 60 cm of Mercury. Density of mercury is 13.6 gram/cm³ and density of water is 1000 kg/m³.

Ans. Pressure due to Mercury= h×ρ×g

           = 60cm × 13600 kg  / m³ × g

     Pressure due to water = h×1000 kgm-³ × g

But both pressures are equal.so,

60 cm ×13600 kg/ m³ × g = h× 1000 kgm-³ × g

⇒60 cm×13600 kgm-³ / 1000 kgm-³ =h

⇒ h= 8.16 m

4. A hydraulic press is used to lift a load of 500 kilogram force when the ratio of the diameters of pump plunger and press plunger is 1:5. Calculate the effort applied on the piston of pump plunger  if the mechanical advantage of the handle of pump plunger is 4. Calculate the effort applied on the handle of pump plunger.

Ans. Load acting on press plunger = 500 kgf

The effort acting on pump  plunger= E

Radius of pump plunger = x

Radius of press plunger= 5x

Load / effort  =  π R² / π r²

500kgf / E = (5x)² / (x)²

E = 20  kgf 

Mechanical advantage of handle of pump plunger = (4)

MA = L / E

E = L/ ME

    ,

E = 20 kgf / 4 ,=5kgf