Chapter 8

NCERT
Class 9
Science
Solutions
6. A stone of 1 kg is thrown with a velocity of 20 ms–1 across the frozen surface of lake and comes to rest after travelling a distance of 50 m. What is the force of friction between the stone and the ice?

Question:

A stone of 1 kg is thrown with a velocity of 20 ms–1 across the frozen surface of lake and comes to rest after travelling a distance of 50 m. What is the force of friction between the stone and the ice?

Answer:

According to question,

m = 1 kg, initial velocity u = 20 ms–1

final velocity v = 0, distance s = 50 m

∴ from the formula         

v2 = u2 + 2as

0 = 202 + (2 x a x 50)

0 = 400 + 100a

-400/100 = a

a = -4 ms–2

Frictional force F = ma

F = 1 X (-4)

F = -4N

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