Question

1. why is it advised to tie any luggage kept on the roof of bus with rope.

2. a stone of 1 kg is thrown with velocity of 20 m s-¹ across the frozen surface of a lake and comes to rest after travlling a distance of 50m. what is the force of friction between the stone and the ice?

class 9 physics questions.
chapter - force and laws of motion.

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Answer 1

Answer:

Explanation:

1. If any luggage kept on the roof of the bus is not tied with a rope, then it tends to move forward due to its inertia. In this process, it could fall off the bus. Therfore, it is advised to tie any luggage kept on the roof of a bus with a rope.

2. Given that,

Mass = 1 kg, Initial Velocity = 20 m/s and Distance travelled = 50 m.

Since the object comes to rest at the end, the final velocity is 0 m/s.

Frictional Force = Mass * Acceleration

=> Acceleration = ?

V² - U² = 2as

=> 0² - 20² = 2 ( 50 ) ( s )

=> -400 = 100 a

=> a = - 400 / 100 = -4 m/s²

Therefore Frictional Force = Mass * Acceleration

=> Force = 1 kg * -4 m/s² = -4 kg.m/s² or -4 N

Hence the frictional force is -4 N.

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