9th Science NCERT Chapter 8
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– First Law of Motion: An object remains in a state of rest or of uniform motion in a straight line unless compelled to change that state by an applied force. This is also known as the law of inertia【4:0†source】.
– Second Law of Motion: The rate of change of momentum of an object is proportional to the applied unbalanced force in the direction of force, expressed as F = ma【4:4†source】.
– Momentum: The momentum of an object is the product of its mass and velocity, having the same direction as that of the velocity. Its SI unit is kg m s^-1. Momentum has both direction and magnitude .
– Third Law of Motion: To every action, there is an equal and opposite reaction, and they act on two different bodies. Action and reaction forces are always equal in magnitude but opposite in direction .
Define the momentum of an object. What is its SI unit?
Explain why it is advised to tie any luggage kept on the roof of a bus with a rope.
Why does a cricket ball slow down and come to rest after being hit by a batsman and rolling on a level ground?
A stone is thrown across a frozen surface of a lake and comes to rest after traveling a distance. What force causes the stone to stop?
Calculate the acceleration and the force acting on a truck rolling down a hill if it covers a distance of 400 m in 20 s with a mass of 7 tonnes.
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