Answer:
2400 kilogram per cubic meter
Explanation:
the density of concrete is a measure of its unit weight.
concrete is a mixture of cement, fine and coarse aggregates, water and sometimes some supplementary materials like fly ash, and various admixtures.
I say around 40% - 60%
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http://www.teendriversource.org/stats/support_teens/detail/57
http://www.rmiia.org/auto/teens/Teen_Driving_Statistics.asp
(I just corrected the question. Sorry if it is still incorrect.)
Answer:
The moment arm is 0.6 m
Explanation:
Given that,
First force 
Second force 
Distance r = 0.2 m
We need to calculate the moment arm
Using formula of torque

So, Here,

We know that,
The torque is the product of the force and distance.
Put the value of torque in the equation


Where,
=First force
=First force
=Second force
= distance
Put the value into the formula


Hence, The moment arm is 0.6 m
Answer:
g' = 10.12m/s^2
Explanation:
In order to calculate the acceleration due to gravity at the top of the mountain, you first calculate the length of the pendulum, by using the information about the period at the sea level.
You use the following formula:
(1)
l: length of the pendulum = ?
g: acceleration due to gravity at sea level = 9.79m/s^2
T: period of the pendulum at sea level = 1.2s
You solve for l in the equation (1):

Next, you use the information about the length of the pendulum and the period at the top of the mountain, to calculate the acceleration due to gravity in such a place:

g': acceleration due to gravity at the top of the mountain
T': new period of the pendulum

The acceleration due to gravity at the top of the mountain is 10.12m/s^2
He needs to improve his endurance time.