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.
Answer:
a = change in v / change in time
= (5.2 - 11) / 3.1
= -1.87 m/s^2
Explanation:
Consider the upward direction of motion as positive and downward direction of motion as negative.
a = acceleration due to gravity in downward direction = - 9.8 
v₀ = initial velocity of rock in upward direction = ?
v = final velocity of rock at the highest point = 0 
t = time to reach the maximum height = 4.2 sec
Using the kinematics equation
v = v₀ + a t
inserting the values
0 = v₀ + (- 9.8) (4.2)
v₀ = 41.2 