i. Newton's first law of motion is valid only in the absence of




... Answer is (b)  net force
According to Newton's first law of motion, a body continues its state of rest or of uniform motion in a straight line provided no net force act on it. For example, a book lying on the table remains at rest as long as no net force act on it. Similarly, a moving object does not stop moving by itself if there is no force to oppose the motion of a body.


ii. Inertia depends upon




... Answer is (c)  mass
Inertia of a body is its property due to which it opposes any change in its state of rest or motion. It depends solely upon mass. The more mass, the more inertia, and vice versa.


iii. A boy Jumps out of a moving bus. There is a danger of him falling:




... Answer is (c) in the direction of motion
A boy when getting down or jumping out from a moving bus holds the inertia of motion. As the man lands on the ground, his feet quickly rest while the upper part of the body continues to move due to the inertia of motion. Therefore, the person falls forward (in the direction of the Motion of the bus). Note: It is very dangerous to jump out of a moving bus. In such case, if happened, a person should run fast in the direct motion of the bus to avoid falling on the ground.

iv. A string is stretched by two equal and opposite forces of 10 N each. The tension in the string is:




... Answer is (c) 10 N
 According to Newton's 3rd law of motion, action and reaction are equal and opposite. Both applied forces contribute to tension in the string equally as they are both equal and opposite. So the tension in the string is equal to F Newton i.e. 10 N.


v. The mass of a body:




... Answer is (d) none of the above
 The mass of a body is the quantity of matter contained in it. So no change occurs in the quantity of matter either accelerated or decelerated i.e. Mass of the body remains the same.


vi. Two bodies of masses m1 and m2 attached to the ends of an Inextensible string passing over a frictionless pulling such that both move vertically. The acceleration of the bodies is:





... Answer is (b)
Let m1 and m2 be the two masses of body A and Body B. Let body A move downwards. ( m1 > m2). According to Newton's 2nd law. m1g−T=m1a ...... (1) and T - m2g = m2a ...... (2) adding both Eqn 1 and eqn 2 we get. a ={ (m1 - m2) / (m1 + m2) } g ie. Option (b).


vii. Which of the following is the unit of momentum? :




... Answer is (c) Ns
P (Momentum) = mv = kgm/s (1st unit). As Newton's 2nd law of motion in terms of force and momentum is " the rate of change of momentum is called Force". So, F = P / t or P = Ft =Ns (2nd unit).


viii. When a horse pulls a cart, the action is on the :




... Answer is (d) Earth and cart
 When a horse pulls a cart there are two actions. One the horse pushes the ground in a backward direction and 2nd the Horse pulls the cart. So in this question, Earth and the cart is the right answer.


ix. Which of the following material lowers the friction when pushed between metal plates?




... Answer is (d) oil
 Reduce friction, Oil among the four options can more lower the friction when pushed between metal plates.



VIP Note: If you have Learned the above MCQs, then examine yourself by taking this Simple MCQS Quiz (Click here to play the Quiz)



 
Unit 3: Dynamics
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9th Class MCQs Quizzes LIST

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Unit-2    ⇚   9th Physics Content List   ⇛  Unit-4

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