Mechanics

41.Railway tracks are banked on their curves due to
 
A. The horizontal component of the train’s weight is sufficient to obtain the required centrifugal force.
 
B. No force of friction can arise between the wheels of the train and the tracks.
 
C. The required centripetal force can be obtained from the horizontal component of the weight of the train.
 
D. The train cannot fall inwards
 
Option”C” is correct.
Railway tracks are banked at the curves so that the necessary centripetal force may be obtained from the horizontal component of the reaction on the train.
42.Why does a cyclist lean while taking a turn?
 
A. The speed of the cycle and the man should be same or else the cycle will slip.
 
B. cyclist is generating necessary centripetal force, it will prevent it from falling
 
C. It leans so as to apply pressure to the wheels to travel on a curve
 
D. It leans to go over the curve faster
 
Option”B” is correct.
The cyclist bends slightly inwards while going on a curved road because by doing that the cyclist is generating necessary centripetal force, which is being centred towards the centre that helps in turning around a bend. The cyclist leans towards the direction of the curve’s centre of curvature.
43.In which turn does a cyclist turn?
 
A. Leans outward
 
B. Leans in
 
C. Leans forward
 
D. Does not bend at all
 
Option”B” is correct.
A cyclist must lean into a turn to prevent tipping over in the other direction. To see why this is so, consider the sketches below. The sketch on the left represents a cyclist, seen from behind, who is attempting to remain upright while turning to the left.
44.What causes the cream to separate from milk when it is churned vigorously?
 
A. Centrifugal force
 
B. Centripetal force
 
C. Force of gravity
 
D. Frictional force
 
Option”A” is correct.
When the milk is churned centrifugal force acts on it outward and due to which cream in milk is separated from it.
45.When a bucket of water is rotated very fast in a vertical circle, then the water does not fall from the bucket even from its highest position because
 
A. Centrifugal force is greater than the weight of the water
 
B. Centrifugal force is less than the weight of water
 
C. At the highest position of the bucket the weight of the water decreases
 
D. The force of adhesion between the water and the bucket is greater
 
Option”A” is correct.
The weight of the water, which could cause it to fall, is consumed in creating the required centripetal force, and the water does not fall. Because weight supplies the centripetal force, the water does not fall out of the bucket rotated in a vertical circle at the highest point.
46.The working principle of washing machine is
 
A. Substation
 
B. Dialysis
 
C. Centrifugation
 
D. Diffusion
 
Option”C” is correct.
It uses the centrifugal force to move the particles to the bottom of the tube. In the above processes, both processes use the centrifugal force and act in the same manner. So, we can say that the working principle of the washing machine is centrifugation
47.What is the reason that there is no atmosphere on the moon
 
A. It is near the earth
 
B. It receives light from the sun
 
C. It orbits the earth
 
D. The escape velocity of gas molecules on it is less than their root mean square velocity.
 
Option”D” is correct.
The escape velocity on the surface of moon is lesser than the RMS velocity of the molecules of gas at the surface temperature of moon. Therefore, the gas molecules escape and hence moon cannot hold an atmosphere.
48.Which of the following works on the basis of conservation of linear momentum?
 
A. Rocket
 
B. Chopper
 
C. Jet
 
D. Plane
 
Option”C” is correct.

  • The Jet engine works on the phenomenon of Conservation of Linear Momentum.
  • It produces a large volume of gases through the combustion of fuel, which is allowed to escape in backward direction through a jet.
  • The backward rushing gas gains large momentum because of high velocity.
  • It thus imparts an equal and opposite momentum to the jet engine.
  • The jet engine, thus, moves forward with high speed.
  • Conservation of Linear Momentum states that a body in motion retains its total momentum (product of mass and vector velocity) unless an external force is applied to it.

49.With what minimum velocity will a rocket be able to cross the earth’s gravity and go into space?
 
A. 11.2 km/s
 
B. 11.2 m/s
 
C. 11.2 km/h
 
D. 10.2 m/s
 
Option”A” is correct.
The amount of velocity needed to escape our planets gravity is approx 11km per second, which is known as escape velocity.
50.The time period of Geostationary Satellite is-
 
A. 9 hours
 
B. 12 hours
 
C. 24 hours
 
D. 28 hours
 
Option”C” is correct.
The period of a geostationary satellite is the same as the period of rotation of earth which is approximately equal to 24 hours or 1 day.

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