# COMEDK UGET 2009 paper solved for Medical Engineering And Dental

## COMEDK - UGET : Physics 2009 Exam

Here are the questions from the 2009 COMEDK UGET questions paper for physics. All questions are with proper explanation.
1. A simple pendulum has a period T inside a lift when it is stationary. The lift is accelerated upwards with constant acceleration 'a'. The period ?
[A] decreases
[B] increases
[C] remains same
[D] becomes infinite

Explanation:

When the lift ascends with acceleration a then apparent value of acceleration due to gravity becomes (g + a) As $T = 2\Pi\sqrt{\frac{t}{g}}$ So the time period decreases.
2. 90 dB sound is 'x' times more intense than 40 dB sound, then x is
[A] 5
[B] 50
[C] 105
[D] 500

Explanation:

3.
A star is moving from the earth with speed V. Change in wavelength (dÎ») observed on Earth is
[A] Î»V/C
[B] Î»V/(C+V)
[C] Î»C/(C+V)
[D] Î»C/V

Explanation:

If the star is moving away from us, its waves are effectively stretched out when they reach Earth, increasing their wavelength. This shifts the star's spectral lines toward the red end of the spectrum. In 1 second there are f waves and these will cover a distance of v + c where c is the speed of light. (Speed = distance/time and time = 1 second)

The apparent wavelength observed on earth in line with the motion is ?a and is given by

?a = (v + c)/f but f = c/? so ?a = (v + c) ? /c = (v/c + 1) ?

so

?a - ? = v? /c differences in
wavelength can be written as ?? so (?a - ? = ??) so ?? = v?/c
4. An open pipe emits fundamental frequency n0 when it emits 3rd harmonic, the pipe can accommodate
[A] 2 nodes 2 antinodes
[B] 3 nodes 4 antinodes
[C] 3 nodes 3 antinodes
[D] 1 node 2 antinodes

Answer: B. 3 nodes 4 antinodes

Explanation:

For waves on string:
• always has nodes on both ends
• fundamental has an an7node in the middle

Higher harmonics have an addi7onal an7node and node.
• number of an7nodes matches the harmonic number

5.
[A] temperature remains constant
[B] pressure remains constant
[C] volume remains constant
[D] there is no transfer of heat

Answer: D. there is no transfer of heat

Explanation:

An adiabatic process is one that occurs without transfer of heat or matter between a system and its surroundings
6. carnot's heat engine takes 300J of heat from a source at 627oC and gives some part of it to sink at 27oC. Work done by engine in one cycle is
[A] 200J
[B] 300J
[C] 150J
[D] 120J

Explanation:

$W = Q \frac{(T_{1} - T_{2})}{T_{1}} = 300 \times \frac{(900-300)}{900} = 200J$
7. 15/16th of a radioactive sample disintegrates in 2 hrs. Mean life of radioactive sample is approximately,
[A] 30min
[B] 43min
[C] 21min
[D] 15min

Explanation:

8. Clear images of soft tissues can be well studied using
[A] MRI
[B] X-rays
[C] Ultrasonic
[D] I.R rays

Explanation:

Magnetic resonance imaging (MRI) is a noninvasive medical test that helps physicians diagnose and treat medical conditions. MRI uses a powerful magnetic field, radio frequency pulses and a computer to produce detailed pictures of organs, soft tissues, bone and virtually all other internal body structures.
9.
Particles which are note composite and hence truly elementary are
[A] mesons
[B] protons
[C] neutrons
[D] leptons