i. Newton's first law of motion is valid only in the absence of
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
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 for him to fall:
A boy when getting down or jumping out from a moving bus holds the inertia of motion. As the man lands on the ground, while the upper part of the body continue to move due to inertia of motion. Therefore, the person may fall forward (in the direction of Motion of bus). Note: It is very dangerous to jump out of a moving bus. In such case if happened, a man should run fast in the direction 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:
According to Newtons 3rd laws 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 tension in the string is equal to F Newton i.e. 10 N.
v. The mass of a body:
The mass of a body is the quantity of matter contained in it. So no change occur 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:
Let m1 and m2 are the two masses of body A and Body B. Let the body A moves 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?
:
P (Momentum) = mv = kgm/s (1st unit). As Newton 2nd law of motion in term 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 horse pulls a cart, the action is on the :
When a horse pulls a cart there are two actions. One the horse pushes the ground in a backward direction and 2nd the Horse pull the cart. So in this question Earth and the cart is the wright answer.
ix. Which of the following material lowers the friction when pushed between metal plates?
To reduce the friction, Oil among the four option can more lower the friction when pushed between metal plates.
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