Force and Laws of Motion

Force and Laws of Motion - NCERT Guide Science Class 9

Q1: An object experiences a net zero external unbalanced force. Is it possible for the object to be travelling with the non-zerovelocity? If yes, state the conditions that must be placed on themagnitude and direction of the velocity. If no, provide a reason.
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Q2: When a carpet is beaten with a stick, dust comes out. Explain, why?
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Q3: : why is it advised to tie any luggage kept on the roof of a bus with a rope?
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Q4: A truck starts from rest and rolls down a hill with constant acceleration. It travels a distance of 400 m in 20 sec. Find its acceleration. Also find the force acting on it if its mass is 7 metric tones.
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Q5: : A stone of 1 kg is thrown with a velocity of 20 ms-1 across the frozen surface of a lake and comes to rest after travelling a distance of 50 m. What is the force of friction between the stone and the ice?
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Q6: : An 8000 kg engine pulls a train of 5 wagons, each of 2000 kg along a horizontal track. If the engine exerts a force of 40000 N and the track offers a friction force of 5000 N, then calculate:
  1. The net accelerating force;
  2. The acceleration of the train; and
  3. The force of wagon 1 on wagon 2.
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Q7: : Using a horizontal force of 200 N, we intend to move a wooden cabinet across a floor at constant velocity. What is the force of friction that will be exerted on the cabinet?
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Q8: Two objects each of mass 1.5 kg are moving in the same straight line but in opposite directions. The velocity of each object is 2.5 ms–1 before the collision during which they stick together. What will be the velocity of the combined object after collision?
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Q9: According to the third law of motion when we push on an object, the object pushes back on us with an equal and opposite force. If the object is a massive truck parked along the roadside, it will probably not move. A student justifies this by answering that the two opposite and equal forces cancel each other. Comment on this logic and explain why the truck does not move.
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Q10: A hockey ball of mass 200 gm travelling at 10 ms–1 is struck by a hockey stick so as to return it along its original path with avelocity at 5 ms–1. Calculate the change of momentum occurred in the motion of the hockey ball by the force applied by the hockey stick.
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Q11: An Object of mass 100 kg is accelerated uniformly from avelocity of 5 ms– 1 to 8 ms–1 in 6 sec. Calculate the initial and final momentum of the object. Also find the magnitude of the force exerted on the object.
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