Question Details

If the momentum of a body increases by 0.01%, its kinetic energy will increase by

Options

A

0.01 %

B

0.02 %

C

0.04 %

D

0.08 %

Correct Answer :

0.02 %

Solution :

The correct option is 0.02 %.

Step 1: Establish the relationship between kinetic energy and momentum
The kinetic energy (K) of a body of mass m moving with velocity v is expressed as:

K = 1 2 m v 2
The momentum (p) of the body is defined as:

p = m v
Rearranging the momentum formula to solve for velocity gives:

v = p m
Substituting this velocity term into the kinetic energy formula yields:

K = 1 2 m p m 2 = p 2 2 m

Step 2: Relate small percentage changes using differentiation
Since the percentage change in momentum is extremely small (0.01%, which is far less than 10%), we can use the differential approximation method to find the corresponding change in kinetic energy.
Taking the natural logarithm (ln) on both sides of the kinetic energy relation:

ln ( K ) = ln p 2 2 m
Applying logarithmic identities, this becomes:

ln ( K ) = 2 ln ( p ) - ln ( 2 m )
Differentiating both sides with respect to their variables (noting that mass m is constant, so ln(2m) differentiates to zero):

d K K = 2 d p p

Step 3: Compute the percentage increase in kinetic energy
Multiplying both sides of the differential relationship by 100 converts the fractional changes into percentage changes:

Δ K K × 100 = 2 × Δ p p × 100
We are given that the percentage increase in momentum is 0.01%:

Δ p p × 100 = 0.01 %
Substituting this value into the percentage relation:

Percentage increase in kinetic energy = 2 × 0.01 % = 0.02 %
Thus, the kinetic energy of the body increases by 0.02%.

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