# 3 and 4 Marks Question

1. What is the condition for an object to sink in water? The cross-sectional area of piston A1 and A2 is 50cm2 and 0.2m2 respectively. How many load can lift in piston A2 if 250N force is applied on piston A1.
2. When the density of an object is higher than that of water, the object sinks into water.
Here,
The cross-sectional area of piston A1 (A1) = 50 cm2 = 0.005 m2
Force applied in piston A1 (F1) = 250N
The cross-sectional area of piston A2
(A2) = 0.2 m2
Force applied in piston A2 (F2) = ?

Now, According to Pascal's law,
Pressure on the small piston = Pressure on the large piston
or, P1 = P2
or, $\frac{F_1}{A_1}$ = $\frac{F_2}{A_2}$

or, $\frac{250}{0.005}$ = $\frac{F_2}{0.2}$

∴ F2 = 104 N.
3. Study the following diagram and answer the questions.
1. What is the weight of the stone in air?
2. Here,
weight of the stone in air = weight of the stone in water + weight of water displaced
= 20 + 5
= 25N
3. How much upthrust is exerted by water on that stone?
4. Here, upthrust = weight of water displaced
∴ upthrust = 5N
5. What is the mass of that stone?
6. We know,
mass of stone (m) = $\frac{w}{g}$
= $\frac{25}{10}$
= 2.5 Kg
4. An effort of 100N can raise a load of 2000N in a hydraulic press. Calculate the cross-sectional area of a small piston in it. The cross-sectional area of a large piston is 4 m2. Write any one applications of Hydraulic press.
5. Here,
Cross-sectional area of a large piston (A2) = 4m2
Cross-sectional area of a small piston(A1) = ?
Effort in small piston (F1) = 100N
Effort in large piston (F2) = 2000N

Now, According to Pascal's law,
Pressure on the small piston = Pressure on the large piston
or, P1 = P2
or, $\frac{F_1}{A_1}$ = $\frac{F_2}{A_2}$

or, $\frac{100}{A_1}$ = $\frac{2000}{4}$
∴ A1 = 0.2m2

Hydraulic press is used for compressing cotton, extracting oils from seeds, etc.