Question Details

The velocity of a body which hasfallen freely under gravity varies as gᵖhʷ ,where g is the acceleration due to gravity at the place and h is the height through which the body has fallen. Determine the values of p and w..

Options

A

p=-1/2 and q=1/2

B

p=1/2 and q=-1/2

C

p=2 and q=1/2

D

p=1/2 and q=1/2

Correct Answer :

p=1/2 and q=1/2

Solution :

The correct option is p=1/2 and q=1/2 (where q corresponds to the exponent w of height h in the question statement).

To find the values of p and w (referred to as q in the options), we can use the method of dimensional analysis.

Let the velocity of the body be represented by v. According to the problem statement, the velocity varies as gphw. We can write this relation as an equation with a dimensionless constant k:
v=kgphw

Let us write down the dimensions of each physical quantity involved:
1. Dimensions of velocity v (distance/time) are: [v]=[LT-1]
2. Dimensions of acceleration due to gravity g (acceleration) are: [g]=[LT-2]
3. Dimensions of height h (length) are: [h]=[L]
4. The constant k is a dimensionless quantity, so it has no dimensions.

Now, substituting the dimensions of all quantities into our equation:
[LT-1]=[LT-2]p[L]w

Simplifying the right-hand side of the equation:
[L1T-1]=[LpT-2p]·[Lw]
[L1T-1]=[Lp+wT-2p]

For the equation to be dimensionally correct, the exponents of the corresponding dimensions on both sides must be equal.

Equating the power of time T on both sides:
-2p=-1
p=1/2

Equating the power of length L on both sides:
p+w=1

Substitute the value of p=1/2 into the equation:
1/2+w=1
w=1-1/2
w=1/2

By mapping the exponent w from the question to q in the options, we find:
p=1/2 and q=1/2 (since q=w).

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