Answer: Magnes
Explanation: Magnes found that the nails and buckle of his sandals and the tip of his staff were attracted to the rock he was standing on. He dug up the Earth to find lodestones. Lodestones contain magnetite, a natural magnetic material Fe3O4.
Answer:
(a) 19.62 N
(b) Box moves down the slope
(c) 24.43 N
Explanation:
(a)
2 Kg box causes tension
hence
where m is mass and g is gravitational force
T'=4*9.81 sin 35= 22.5071 N
Since T' is greater than
, then the box moves down the slope
(c)
Acceleration a=

When moving, the box will exert force T"=
T"= 4*9.81 sin 35 +(4*0.48)= 24.43 N
Answer:
775.48 W
Explanation:
given,
diameter of disk = 0.6 cm
length of the disk = 0.4 m
T₁ = 450 K T₂ = 450 K T₃ = 300 K
= 1.33
now,
the value of view factor (F₁₂)corresponding to 1.33
F₁₂ = 0.265
F₁₃ = 1 - 0.265 = 0.735
now,
net rate of radiation heat transfer from the disk to the environment:

= 2 F₁₃ A₁ σ (T₁⁴ - T₃⁴)
= 2 x 0.735 x π x (0.3)² x (5.67 x 10⁻⁸ W/m²) (450⁴ - 300⁴)
= 775.48 W
Net radiation heat transfer from the disks to the environment = 775.48 W