Answer:

Explanation:
Given:
- length of the concrete slab,

- temperature of observation,

- we've the coefficient of linear expansion for concrete,

- lower temperature limit,

- upper temperature limit,

<u>Change in length due to temperature can be given as:</u>



<u>Now at temperature 15°C:</u>

Hence the expansion crack between the slabs at this temperature must be:



1,2,5 are correct answers.
Answer:
Explanation:
Near the earth's surface where gravity is approximately 10 m/s² downward
v = u + at
v = 5 + (-10)(1) = -5 m/s
so it has the same speed but in the opposite (downward) direction.
The force of friction is equal to the pushing force, and the acceleration is zero
Explanation:
In this problem, we are pushing a piano along the floor, in the horizontal direction.
There are 2 forces acting in the horizontal direction on the piano:
- The applied force,
, acting forward - The force of friction,
, acting backward
Therefore, the net force in the horizontal direction is

According to Newton's second law, the net force is equal to the product between the piano's mass (m) and its acceleration:

Combining the two equations,

However, we are also told that the piano moves at constant speed, therefore the acceleration is zero:

And so,

which means that the force of friction is equal to the applied force.
Learn more about Newton's second law:
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