Answer: C. unknown element he predicted would have properties similar to those of aluminum.
Explanation: Mendeleev arranged the elements in order of increasing atomic masses. He left spaces for the elements that were predicted to exist, but were not discovered.
One space was left below Aluminum where an element of mass 70 was predicted to exist with properties similar to Aluminum. It was referred to as eka-Aluminum.
Later it was named as gallium.
With 30degree because incident angle = reflected angle
Answer:
a) 250 N/m
b) 22.4 rad/s , 3.6 Hz , 0.28 sec
c) 0.3125 J
Explanation:
a)
F = force applied on the spring = 7.50 N
x = stretch of the spring from relaxed length when force "F" is applied = 3 cm = 0.03 m
k = spring constant of the spring
Since the force applied causes the spring to stretch
F = k x
7.50 = k (0.03)
k = 250 N/m
b)
m = mass of the particle attached to the spring = 0.500 kg
Angular frequency of motion is given as


= 22.4 rad/s
= frequency
Angular frequency is also given as
= 2 π
22.4 = 2 (3.14) f
= 3.6 Hz
= Time period
Time period is given as


= 0.28 sec
c)
A = amplitude of motion = 5 cm = 0.05 m
Total energy of the spring-block system is given as
U = (0.5) k A²
U = (0.5) (250) (0.05)²
U = 0.3125 J
Answer:
They're calibrated to measure, liquids of greatest density.
Explanation: