The force that the book exerts on the table is a normal force, not a weight force. (The book's weight doesn't act on the table, it acts on the book.) It's equal in magnitude to the weight of the book, again, because of the first law.
Explanation:
First, find the velocity of the projectile needed to reach a height h when fired straight up.
Given:
Δy = h
v = 0
a = -g
Find: v₀
v² = v₀² + 2aΔy
(0)² = v₀² + 2(-g)(h)
v₀ = √(2gh)
Now find the height reached if the projectile is launched at a 45° angle.
Given:
v₀ = √(2gh) sin 45° = √(2gh) / √2 = √(gh)
v = 0
a = -g
Find: Δy
v² = v₀² + 2aΔy
(0)² = √(gh)² + 2(-g)Δy
2gΔy = gh
Δy = h/2
Answer:
Gravity is an attractive force as well as electromagnetic, but electromagnetic attracts and repels.
Explanation:
Answer:
This conveyor belt should be connected to fixed pulleys in case their total effort is less than the load. But if it's not that, the belt should be connected to movable pulleys.
Explanation:

Answer:
The choice of building materials and techniques can help them cool down faster, after heating up is explained below in brief details.
Explanation:
Building materials
Buildings that are composed of rock, bricks, or pavement, or inserted into the territory, can seem cooler thanks to the great "thermal mass" of these elements – that is, their capability to assimilate and discharge heat gently, thereby softening temperatures over time, producing daytime cooler and night-time warmer.