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problem is that we don’t
notice the third body-
the Earth. Namely, due to
interaction Earth-horse

the horse with sleigh
moves on the surface of
the Earth

Figure 3.3

4.3 Questions

1. What does Newton's first law state?

2. What's inertial frame of refrence?
3. What does Newton's second law state?
4. A question is a joke ."It's not the fall that hurts you, it's the sudden

stop at the bottom".Translate this saying into the language of Newton's
laws of motion?
5.What does principle of forces superposition mean?

6.What does unit of force 1N mean?
7.What does s Newton's third law state?
3.5 Problems

1. A block, which mass is 10 kg, rests in a horizontal surface. What
horizontal force F is required to
x
give it a velocity of 2 m in
s

s 2 ?Assume that the block starts from
the rest .Tthe factor of friction
between the block and the surface is
equal to   , 0 05

Solution
Figure 4.3 The mass of block is given. The
y-component of it’s acceleration is

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