Question

Камень брошен горизонтально с обрыва высотой 20м, упал на расстоянии 28м от точки бросания. Определите начальную скорость. СРОЧНО!

Answer 1

H=gt²/2
Отсюда время падения t=1,4 с
Если камень за это время пролетел 1000 м, то он был брошен со скоростью 1000/1,4=710 м/c. Это уж скорее не брошен, а выcтрелен.

Answer 2

Problem Analysis

We are given that a stone is thrown horizontally from a cliff with a height of 20m and lands at a horizontal distance of 28m from the throwing point. We need to determine the initial velocity of the stone.

Solution

To solve this problem, we can use the kinematic equation for horizontal motion:

Δx = v₀ * t

where: - Δx is the horizontal distance traveled by the stone (28m in this case) - v₀ is the initial velocity of the stone (what we need to find) - t is the time of flight of the stone

Since the stone is thrown horizontally, its initial vertical velocity is zero. Therefore, the time of flight can be determined using the equation for vertical motion:

Δy = v₀y * t + (1/2) * g * t²

where: - Δy is the vertical distance traveled by the stone (20m in this case) - v₀y is the initial vertical velocity of the stone (zero in this case) - g is the acceleration due to gravity (approximately 9.8 m/s²)

Simplifying the equation, we get:

Δy = (1/2) * g * t²

Substituting the values, we have:

20 = (1/2) * 9.8 * t²

Solving for t, we find:

t² = (20 * 2) / 9.8

t² = 40 / 9.8

t² ≈ 4.08

Taking the square root of both sides, we get:

t ≈ √4.08

t ≈ 2.02 seconds

Now that we have the time of flight, we can substitute it back into the horizontal motion equation to find the initial velocity:

28 = v₀ * 2.02

Solving for v₀, we find:

v₀ = 28 / 2.02

v₀ ≈ 13.86 m/s

Therefore, the initial velocity of the stone is approximately 13.86 m/s.

Answer

The initial velocity of the stone when thrown horizontally from a cliff with a height of 20m and landing at a horizontal distance of 28m from the throwing point is approximately 13.86 m/s.