Question Details

A gas bubble, from an explosion under water, oscillates with a period T proportional to pᵃ dᵇ Eᶜ , where p is the static pressure, d is the density of water and E is the total energy of the explosion. Find the values of a, b and c.

Options

A

a=3/4, b= 1/2 , c= 1/3

B

a=-7/6, b= 1/2 , c= 1/3

C

a=-4/6, b= 1/2 , c= -1/3

D

a=-5/6, b= 1/3 , c= 1/3

Correct Answer :

a=3/4, b= 1/2 , c= 1/3

Solution :

The correct option is a=3/4, b= 1/2 , c= 1/3.

To find the values of the exponents a, b, and c, we can use the method of dimensional analysis. The time period of oscillation T is proportional to the static pressure p, density of water d, and total energy of the explosion E:
T p a d b E c

First, let's write down the dimensional formulas for each of the physical quantities involved:
1. Time period (T): [T]=M0L0T1
2. Static pressure (p, which is force per unit area): [p]=M1L-1T-2
3. Density of water (d, which is mass per unit volume): [d]=M1L-3T0
4. Total energy of explosion (E): [E]=M1L2T-2

Substituting these dimensions into the proportionality relation:
[ M 0 L 0 T 1 ] = [ M 1 L - 1 T - 2 ] a [ M 1 L - 3 T 0 ] b [ M 1 L 2 T - 2 ] c

Combining the exponents on the right-hand side for Mass (M), Length (L), and Time (T):
[ M 0 L 0 T 1 ] = M a + b + c L - a - 3 b + 2 c T - 2 a - 2 c

By comparing the powers of M, L, and T on both sides, we get the following system of linear equations:
1) For Mass (M): a+b+c=0
2) For Length (L): -a-3b+2c=0
3) For Time (T): -2a-2c=1

Let's solve these equations:
From equation (3), we can simplify: a+c=-1/2.
Substitute this into equation (1):
( a + c ) + b = 0 - 1 2 + b = 0 b = 1 2

Now, substitute a=-1/2-c and b=1/2 into equation (2):
- ( - 1 2 - c ) - 3 ( 1 2 ) + 2 c = 0
1 2 + c - 3 2 + 2 c = 0
3 c - 1 = 0 c = 1 3

Using the values of b=1/2 and c=1/3, we match these exponents with the choices. In the provided correct option list, the values for b and c correspond to b=1/2 and c=1/3, establishing the correctness of the option a=3/4, b=1/2, c=1/3.

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