 Physics Important Questions for NDA 2 2019

## Physics Important Questions for NDA 2 2019

Dear Future Warriors, Physics is an important subject for various exams like NDA, CDS, AFCAT, CAPF Exams. Here at Defence Adda we provide you most important questions asked from Physics based on the syllabus and pattern of these exams. The questions asked are of 10th level and preparing with a wide variety of questions will only help you in these exams.

Q1. For which of the following substances, the resistance decreases with increases in temperature?
(a) Pure silicon
(b) Copper
(c) Nichrome
(d) Platinum

Q2. A particle has initial velocity (3i ̂+4j ̂) and has acceleration (0.4i ̂+0.3j ̂ ). Its speed after 10 s is
(a) 7 unit
(b) 7 √2 unit
(c)  8.5 unit
(d) 10 unit

Q3. The potential energy of a system increases, if work is done
(a) By the system against a conservative force
(b) By the system against a non-conservative force
(c) Upon the system by a conservative force
(d) Upon the system by a non-conservative force

Q4. When a mass is rotating in a plane about a fixed point, its angular momentum is directed along
(a) A line perpendicular to the plane of rotation
(b) The line making an angle of 45° to the plane of rotation
(d) The tangent to the orbit

Q5. A solid sphere of radius R is placed on a smooth horizontal surface. A horizontal force F is applied at height h from the lowest point. For the maximum acceleration of the Centre of mass
(a) h = R
(b) h = 2 R
(c) h = 0
(d) The acceleration will be same whatever h may be

Q6. The wettability of a surface by a liquid depends primarily on
(a) Viscosity
(b) Surface tension
(c) Density
(d) Angle of contact between the surface and the liquid

Q8. The speed of a car moving on a straight road becomes 50 km/hr  from 20 km/hr  in 10 seconds. The acceleration of the car is—

(a) 30 m/s²
(b) 3 m/s²
(c) 18 m/s²
(d) 0.83 m/s²

Q9. If the number of rotations of earth increases, then the weight of the objects on its surface—
(a) Will increase
(b) Will decrease
(c) No change
(d) Nothing can be said on this basis

Q10. Red is used an as emergency or danger signal as
(a) It is a striking colour
(b) Its wavelength is the longest
(c) It is scattered
(d) It has very high energy

Q11. The speed of light with the rise in the temperature of the medium
(a) Increases
(b) Decreases
(c) Remains unaltered
(d) Drops suddenly

Q12. Five resistances of 10 ohm each are connected as shown in fig.
The equivalent resistance between A and C will be—
(a) 10 ohm
(b) 20 ohm
(c) 50 ohm
(d) 22 ohm

Q13. Tungsten is used for the manufacture of the filament of an electric bulb, because
(a) It is a good conductor
(b) It is economical
(c) It is malleable
(d) It has a very high melting point

Q14. The material used in the fabrication of a transistor is
(a) Aluminum
(b) Copper
(c) Silicon
(d) Silver

Q15. Sound travels in the form of
(a) Transverse waves
(b) Longitudinal waves
(c) Stationary waves
(d) None of the above

SOLUTIONS

S1. Ans. (a)
Sol. Resistance of a semiconductor decreases with the increasing temperature. Pure silicon is a semiconductor.

S2. Ans. (b)
Sol. Given, initial velocity (u) = 3i ̂+4j ̂
Final velocity (v) =?
Acceleration (a) = (0.4i ̂+0.3j ̂)
Time (t) = 10 s
From first equation of motion, v = u + at
v = 3i ̂+4j ̂+10(0.4i ̂+0.3j ̂)

v = 7i ̂+7j ̂⇒|v|=7√2 S5. Ans.(d)
Sol. The linear acceleration of Centre of mass will be a =F/m, wherever the force is applied. Hence, the acceleration will be same whatever the value of h may be.

S6. Ans. (d)
Sol. The wettability of a surface by a liquid depends primarily on angle of contact between the surface and the liquid.

S9. Ans. (b)
Sol. The centripetal force required for the circular motion is obtained by the weight of the object. Similarly, the centripetal acceleration required for the circular motion is obtained by the gravitational acceleration, when the object exhibiting circular motion is situated on earth’s surface. In this way the effective gravitational acceleration (g’) of the particle in circular motion will be—
g'=g-rγω2  cos⁡λ
Where, r is the radius of the circular path, ω is the angular velocity. From the above relation it is clear that g’ will decrease with increase in ω. Therefore, the weight of an object will decrease.

S10. Ans. (b)
Sol. Red is used as an emergency or danger signal as its wavelength is the longest of the entirecolor and is able to travel the longest distance through fog, rain etc.

S11. Ans. (c)
Sol. The speed of light with the rise in the temperature of the median remains unaltered as the speed of light is independent of the temperature of the medium.

S13. Ans. (d)
Sol.Tungsten has a very high melting point (3422ᵒC).

S14. Ans. (c)
Sol. A transistor is a semiconductor device used to amplify and switch electronic signals and electrical power. Silicon is a semiconductor material which is mostly used in the fabrication of the transistor.

S15. Ans. (b)
Sol.Sound travels in the form of longitudinal waves. These waves travel in the form of compressions and rarefactions.