Physics [Laws Of Motion] Questions for Railway ALP Stage-II Exam : 21st November 2018

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Q1. If the horizontal range of projectile is four times its maximum height, the angle of projection is?
यदि प्रक्षेप्य की क्षैतिज सीमा इसकी अधिकतम ऊंचाई से चार गुना है, तो प्रक्षेपण का कोण है?
(a)  30°
(b) 45°
(c) sin^(-1)⁡(1/4)
(d) tan^(-1)⁡(1/4)
Show Answer
Maximum height (H) =(u^2 sin^2 θ)/2g
Horizontal range (R) = (u^2 sin^2 2θ)/g
According to question, R = 4H
(u^2 sin^2 2θ)/g=4.(u^2 sin^2 θ)/2g
Sin²2θ = 2 sin²θ
(2 sinθ.cosθ)² = 2 sin²θ
⇒(4sin^2 θ.cos^2⁡θ)/(sin^2 θ)=2
⇒cos^2 θ=1/2⇒cosθ=1/√2 

Q2. Object with a constant speed
स्थिर गति के साथ वस्तु
(a) Is not accelerated/ त्वरित नहीं होती है
(b) Might be accelerated/ त्वरित हो सकती है
(c) Is always accelerated/ हमेशा त्वरित होती है
(d) Also has a constant velocity/ एक स्थिर वेग भी है

Show Answer
S2. Ans.(c)
Sol.  An object can accelerate while traveling at constant speed but not at constant velocity. This is because acceleration is a measure of the change in velocity over time.Therefore, at a constant speed (meaning no change in the magnitude of the velocity) an object could be changing its direction, and thus, accelerating.

Q3. A man in a train moving with a constant velocity drops a ball on the platform. The path of the ball as seen by an observer standing on the platform is?
एक निश्चित गति के साथ चलने वाली एक ट्रेन एक प्लेटफ़ॉर्म पर एक गेंद फेंकती  है. प्लेटफ़ॉर्म पर खड़े एक पर्यवेक्षक को गेंद का मार्ग दिखाई देता है:
(a) A straight line /एक सीधी रेखा
(b) A circle /एक वृत्त
(c) A parabola /एक अनुवृत्त
(d) None of these /इनमें से कोई नहीं

Show Answer
Sol. Say the train moves in the X-direction, the ball is thrown into the Y-direction and it the Z-direction is up-down.
If you are an observer such that the train is moving with respect to you, you will see the ball moving with a constant velocity in X and Y, but also seeing it start to fall down. So, you see a parabola in a plane that is cross wise to the axis.

Q4. An object covers distance which is directly proportional to the square of the time. Its acceleration is
एक वस्तु दूरी तय करती है जो उस समय के वर्ग के लिए सीधे आनुपातिक होती है. इसका त्वरण है-
(a) increasing/बढ़ता है
(b) decreasing/घटता है
(c) zero/शून्य
(d) constant/स्थिर रहता है

Show Answer
s=ut+1/2 at^2
u = initial velocity
a = acceleration
t = time
s = displacement
if initial  speed is zero i.e., u = 0
then, ut = 0
so, s  =1/2 at²
if, a is constant, then s ∝ t².

Q5. When the milk is churned vigorously, the cream from it separated out due to 
मंथन द्वारा दूध से क्रीम का पृथक्करण _______ के कारण होता है: 
(a) gravitational force/ गुरुत्वाकर्षण बल
(b) frictional force/ घर्षण बल
(c) centrifugal force/ अपकेन्द्रीय बल
(d) centripetal force/ केन्द्राभिमुख शक्ति

Show Answer
Sol. When the milk is churned vigorously the cream from it is separated out duel the effect of centrifugal force as when liquids of different specific gravities revolve around the same centre at I same distance and with the same angular velocity, then a huge centrifugal force is exerted on the heavier ;al than on the lighter one.

Q6. The function of ball bearing in a wheel is 
एक पहिये में बॉल बेअरिंग का क्या कार्य है?
(a) to increase frivtion/ घर्षण बढ़ाने के लिए
(b) to convert kinetic friction into rolling friction/ काइनेटिक घर्षण को रोलिंग घर्षण में परिवर्तित करने के लिए
(c) to convert statics friction into kinetic friction/ स्थैतिक घर्षण को काइनेटिक घर्षण में परिवर्तित करने के लिए
(d) just for convenirnce/ केवल सुविधा के लिए

Show Answer
Sol.  It convert kinetic friction into the rolling friction which being very small,causes much less energy loss.

Q7. When a running car stops suddenly, the passengers tends to lean forward because of –
जब एक चलती कार अचानक बंद हो जाती है, तो यात्री _______ की वजह से आगे कि ओर गिरता है-
(a) Centrifugal force / अपकेन्द्रीय बल
(b) Inertia of rest/विश्राम का जड़त्व
(c) Inertia of motion/गति का जड़त्व
(d) Gravitation force /गुरुत्वाकर्षण बल
(d) Charge/ चार्ज
Show Answer
Sol. According to the Newton’s first law of motion we know that the inertia of motion is that property of that uniformly moving body due to which it resists a change in its state of uniform motion.
Therefore, the passengers of a running car lean forward when that car stops suddenly.
Q8. The working of a rocket is based on the principle of –
किसी रॉकेट के काम करने का सिद्धांत किस पर आधारित है:
(a) Conservation of momentum / संवेग का संरक्षण
(b) Conservation of mass/ द्रव्यमान का संरक्षण
(c) Conservation of energy/ ऊर्जा का संरक्षण
(d) Conservation of angular momentum/ कोणीय संवेग का संरक्षण
Show Answer
Sol. The working of a rocket is based on the principle of conservation of momentum as in the absence of external forces, the total momentum of the system remains conserved.
here. just before launching, the momentum of the rocket is zero and the rocket is fired it forces a jet of hot gases with a high velocity.
The results the jet of gases acquiring a momentum downwards.
Therefore, the rocket acquires a momentum of equal magnitude in opposite direction which causes the rocket moving  upward

Q9. Angle of friction and angle of repose are?
घर्षण का कोण और विश्राम के कोण ________ होते हैं –
(a) Equal to each other /एक दूसरे के बराबर
(b) Not equal to each other /एक दूसरे के बराबर नहीं
(c) Proportional to each other /एक दूसरे के लिए समानुपातिक
(d) None of the above /उपरोक्त में से कोई भी नहीं
Show Answer
Sol.  Angle of friction is equal to angle of repose.

Q10. The angle, in which a cricket ball should be hit to travel maximum horizontal distance, is 
किस कोण पर, अधिकतम क्षैतिज दूरी तय करने के लिए एक क्रिकेट बॉल मारा जाना चाहिए  है-
(a) 60° with horizontal/ क्षैतिज के साथ 60 डिग्री
(b) 45° with horizontal/ क्षैतिज के साथ 45 डिग्री
(c) 30° with horizontal/ क्षैतिज के साथ 30 डिग्री
(d) 15° with horizontal/ क्षैतिज के साथ 15 डिग्री
Show Answer
Sol.  We know that the formula for horizontal distance in case of projectile motion can be represented as (U^2 sin2θ)/g where, θ  is the angle of projection.
Here, the cricket ball is a projectile and in order to travel the maximum horizontal distance, the ball should be hit at the angle of 45° with horizontal as the maximum value of sin2θ is θ1. (When θ = 45°, then 2θ = 2 x 45° = 90° and sin 90° = 1).

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