Tips and Tricks of The Day


Record Limit : 

    2019-01-17 15:46:44.0
Ex: A body of mass 2 kg moving with a velocity of 3 m/sec collides head on with a body of mass 1 kg  moving in opposite direction with a velocity of 4 m/sec. After collision, two bodies stick together and move with a common velocity which in m/sec  is equal to 
A) 1/4      
B) 1/3
C) 2/3      
D) 3/4
Correct answer: C
Explanation: m1v1−m2v2 = (m1 + m2)v Þ 2 × 3 − 1 × 4 = (2+1)v | Þ v = 2/3 m/s
    2019-01-16 13:01:40.0
Ex: If NaOH is added to an aqueous solution of zinc ions, a white precipitate appears and on adding excess NaOH, the precipitate dissolves. In this solution zinc exists in the 
A) Cationic part
B) Anionic part
C) Both in cationic and anionic parts
D) There is no zinc in the solution
Correct answer: D
Explanation: Zn2+ + 2NaOH → Zn(OH)2 + 2Na+ | Zn(OH)2 + 2NaOH → Na2ZnO2 + 2H2O.
    2019-01-15 12:17:18.0
Ex: From a newly formed radioactive substance (Half life 2 hours), the intensity of radiation is 64 times the permissible safe level. The minimum time after which work can be done safely from this source is 
A) 6 hours                                   
B) 12 hours
C) 24 hours                                 
D) 128 hours
Correct answer: B
Trick:
N / N0 = (1/2)n ⇒ 1 / 64 = (1/2)6 = (1/2)n ⇒ n = 6
After 6 half lives intensity emitted will be safe. Total time taken = 6 × 2 = 12hrs.
    2019-01-14 12:52:31.0
Ex: The optically active tartaric acid is named as  D-(+)- tartaric acid because it has a positive
A) Optical rotation and is derived from D-glucose
B) pH in organic solvent
C) Optical rotation and is derived from D(+) glyceraldehyde
D) Optical rotation only when substituted by deuterium
Correct answer: C
Explanation: D(+)-tartaric acid has positive optical rotation and is derived from D (+) glyceraldehyde.
    2019-01-09 10:44:52.0
Ex: Calculate the work done, if a wire is loaded by 'Mg' weight and the increase in length is 'l' 
A) Mgl         
B) Zero
C) Mgl/2 
D) 2Mgl
Correct answer: C
Explanation:
Work done = 1 / 2 Fl = Mgl / 2
    2019-01-08 12:37:05.0
Ex: A catalyst is a substance which                                     
A) Increases the equilibrium concentration of the product
B) Changes the equilibrium constant of the reaction
C) Shortens the time to reach equilibrium
D) Supplies energy to the reaction
Correct answer: C
Explanation: A catalyst is a substance which alters the rate of reaction and shortens the time to reach equilibrium.
    2019-01-07 12:02:27.0
Ex: A liquid cools down from 70oC to 60oC in 5 minutes. The time taken to cool it from 60oC to 50oC will be
A) 5 minutes                              
B) Lesser than 5 minutes
C) Greater than 5 minutes   
D) Lesser or greater than 5 minutes depending upon the density of the liquid
Correct answer: D
Explanation : According to Newton's law of cooling Rate of cooling µ mean temperature difference. Initially, mean temperature difference = (70 + 60 / 2 − θ0) = (65 − θ0) Finally, mean temperature difference
= (60 + 50 / 2 − θ0) = (55 − θ0) In second case mean temperature difference decreases, so rate of fall of temperature decreases, so it takes more time to cool through the same range.
    2019-01-04 14:03:56.0
Ex: Rusting of iron is catalysed by which of the following
A)  Fe   
B)  O2
C)  Zn   
D)  H+
Correct answer: D
Explanation : Rusting of iron is catalysed by [H+].
    2019-01-03 15:33:52.0
Ex: A convex lens makes a real image 4 cm long on a screen. When the lens is shifted to a new position without disturbing the object, we again get a real image on the screen which is 16 cm tall. The length of the object must be
A) 1/4 cm                                    
B) 8 cm
C) 12 cm                                      
D) 20 cm
Correct answer: B
Explanation: O = √I1I2 = √4×16 = 8cm
    2019-01-02 11:57:13.0
Ex: In an amplifier the load resistance RL is equal to the plate resistance(rp). The voltage amplification is equal to
A) μ                                 
B) 2μ
C) μ/2                             
D) μ/4
Correct answer: C
Explanation : 
Voltage gain Av = μ / 1 + rp / RL, for rp = RL Þ Av = μ/2