MOCK TEST FOR CPET - 2

 

Q/1. If in an elastic collision, a massive particle collides against a lighter One at rest ?

(a) it can never bounce back along its original path

 (b) it may bounce back along its original path

(c) the two particles move at right angles to each other after collision

 (d) None of the above

Ans : P_{before collision} =  mu    but v = -u

  P_{after collision} = mv

 ∆P  =mu – (-mu) =2mu

Option (a) is correct

Q/2. In one-dimensional elastic collision of two particles, the ratio of velocities of separation and approach is equal to ?

(a) coefficient of restitution               

(b) negative of coefficient of restitution

 (c) zero, if collision is perfectly elastic

(d) infinite

 Ans :  coefficient of restitution ;  e = (v₂ -v₁)/(u₂ – u₁)

 

Q/3. In which of the following conditions, the total linear momentum of the system remains constant?

(a) If the resultant external force acting on the system of particles is zero

 (b) If the resultant external force acting on the system of particles is positive

(c) If the resultant external force acting on the system of particles is -ve

(d) None of these

 Ans :    if  F =0

             dp/dt  =0

                   ∆P  =0 ;  P₁ = P₂   

the resultant external force acting on the system of particles is zero

Q/4. From the nozzle of a rocket 100kg of gases are exhausted per sec with a velocity of 1000 / sec m . What force (thrust) does the gas exert on the rocket?

 (a) 100 kg/sec                       (b) 10⁵ Newton

(c) 10³ Newton                       (d) 10² Newton

 Ans :  Exhausted force = u(dm/dt)= 1000*100 =10⁵ N

Q/5. If a particle is at rest relative to an observer at rest at the centre of a rotating frame of reference ?

 (a) centrifugal and Coriolis forces both act

 (b) only centrifugal force acts

 (c) only Coriolis force acts

(d) None of these

Ans : F_rotational = F +F_fic

            F_fic  = -2mΩ*V_rot  - mΩ* (Ω * r)

              V_rot = 0 (given that particle is in rest in rotational form)

              F_fic = - mΩ(Ω*r)   ;      only centrifugal force

Q/6. The length of a rod, of length 5m in a frame of reference which is moving with 0.6 c velocity in a direction making 30⁰ angle with the rod is nearly ?

(a) 4.3m               (b) 3.4 m            (c) 2.43 m             (d) 2.34 m  

Ans :    v_{along rod} = vcos 30 =0.6c*(√3/2)  = 0.3*√3c

                L= L₀ √(1 – v²/c²) =  5*√(1- 0.27c²/c²) = 4.3m

Q/7. The speed of an electron having kinetic energy 2 MeV will be ?

 (a) 2.93*10⁸ m/sec             (b) 3*10⁸ m/sec

  (c)10⁸ m/sec                        (d) 1.5 *10⁸sec   

Ans :   K.E. = 2MeV

          M₀c² = 0.511MeV    ;  KE = (γ -1)M₀c²

          2 = (γ-1)*0.511

               γ = 5   ;    γ= 1/√(1 – v²/c²)  

                     1/25 = (1 – v²/c²)

                   V = 0.98c = 2.93*10⁸  m/sec

     Q/8. Which of the following is true about liquid flow through a capillary tube?

(a)The velocity of the liquid layer in contact with the capillary tube is least

(b) The velocity of the liquid layer in contact with the capillary tube is maximum

(c) The velocity of the liquid layer at the centre of the capillary tube is minimum

(d) None of these

Ans : Velocity of layer increases as layers moves away from contact surface. Velocity of liquid layer in contact with capillary is least

Q/9. The depletion region is created by ?

 (a) ionization                (b) diffusion

(c) recombination          (d) (a), (b) and (c)

 Ans : The depletion region is created by recombination

 

Q/10. A silicon diode is in series with a 1kW resistor and a 5V battery. If the anode is connected to the +ve battery terminal, the cathode voltage with respect to the negative battery terminal is ?

(a) 0.7 V                 (b) 0.3 V  

(c) 5.7V                    (d) 4.3V

 Ans : Silicon diode act like battery of 0.7V with opposite polarity in forward bias. So V = 5 - 0.7 = 4.3 volt.