Math Problem Statement

Một vật được ném theo phương ngang, sau thời gian 0,5s vật rơi cách vị trí ném 5m. Tìm: (a) Độ cao của nơi ném vật, (b) Vận tốc lúc ném vật, (c) Vận tốc khi chạm đất, (d) Vận tốc của vật sau khi ném 0,2s, (e) Góc hợp bởi phương vận tốc và phương ngang sau khi ném 0,2s. Lấy g = 10 m/s².

Solution

Let's solve this step by step based on the question provided:


Given:

  1. Time for the object to fall: t=0.5st = 0.5 \, \text{s}
  2. Horizontal distance traveled: x=5mx = 5 \, \text{m}
  3. Gravitational acceleration: g=10m/s2g = 10 \, \text{m/s}^2

(a) Height of the throw:

The vertical motion is governed by the equation: h=12gt2h = \frac{1}{2} g t^2 Substitute g=10m/s2g = 10 \, \text{m/s}^2 and t=0.5st = 0.5 \, \text{s}: h=1210(0.5)2=12100.25=1.25mh = \frac{1}{2} \cdot 10 \cdot (0.5)^2 = \frac{1}{2} \cdot 10 \cdot 0.25 = 1.25 \, \text{m}

Answer (a): Height = 1.25m1.25 \, \text{m}


(b) Initial horizontal velocity:

The horizontal motion equation is: x=vxtx = v_x \cdot t Rearranging for vxv_x: vx=xtv_x = \frac{x}{t} Substitute x=5mx = 5 \, \text{m} and t=0.5st = 0.5 \, \text{s}: vx=50.5=10m/sv_x = \frac{5}{0.5} = 10 \, \text{m/s}

Answer (b): Initial velocity = 10m/s10 \, \text{m/s}


(c) Velocity when the object hits the ground:

The velocity components are:

  • Horizontal: vx=10m/sv_x = 10 \, \text{m/s}
  • Vertical (using vy=gtv_y = g \cdot t): vy=100.5=5m/sv_y = 10 \cdot 0.5 = 5 \, \text{m/s}

The total velocity vv is: v=vx2+vy2v = \sqrt{v_x^2 + v_y^2} Substitute vx=10v_x = 10 and vy=5v_y = 5: v=102+52=100+25=125=11.18m/sv = \sqrt{10^2 + 5^2} = \sqrt{100 + 25} = \sqrt{125} = 11.18 \, \text{m/s}

Answer (c): Velocity = 11.18m/s11.18 \, \text{m/s}


(d) Velocity after 0.2 seconds:

  1. Vertical velocity after t=0.2st = 0.2 \, \text{s}: vy=gt=100.2=2m/sv_y = g \cdot t = 10 \cdot 0.2 = 2 \, \text{m/s}
  2. Horizontal velocity remains constant: vx=10m/sv_x = 10 \, \text{m/s}

The total velocity vv: v=vx2+vy2v = \sqrt{v_x^2 + v_y^2} Substitute vx=10v_x = 10 and vy=2v_y = 2: v=102+22=100+4=104=10.2m/sv = \sqrt{10^2 + 2^2} = \sqrt{100 + 4} = \sqrt{104} = 10.2 \, \text{m/s}

Answer (d): Velocity = 10.2m/s10.2 \, \text{m/s}


(e) Angle between velocity and horizontal after 0.2 seconds:

The angle θ\theta is given by: θ=tan1(vyvx)\theta = \tan^{-1} \left( \frac{v_y}{v_x} \right) Substitute vy=2m/sv_y = 2 \, \text{m/s} and vx=10m/sv_x = 10 \, \text{m/s}: θ=tan1(210)=tan1(0.2)\theta = \tan^{-1} \left( \frac{2}{10} \right) = \tan^{-1} (0.2) Using a calculator: θ11.31\theta \approx 11.31^\circ

Answer (e): Angle = 11.3111.31^\circ


Summary of Answers:

(a) h=1.25mh = 1.25 \, \text{m}
(b) vx=10m/sv_x = 10 \, \text{m/s}
(c) v=11.18m/sv = 11.18 \, \text{m/s}
(d) v=10.2m/sv = 10.2 \, \text{m/s}
(e) θ=11.31\theta = 11.31^\circ


Would you like further explanations or visualizations for any of these answers?
Here are five questions to deepen your understanding:

  1. How would the results change if the object were thrown at an angle instead of horizontally?
  2. What would happen if air resistance were included in this problem?
  3. How is the vertical motion independent of the horizontal motion in this scenario?
  4. Can you derive the equations of motion for this kind of problem?
  5. How does the value of gravitational acceleration affect the outcome?

Tip: Always separate the horizontal and vertical motions when solving projectile problems to simplify your calculations!

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Math Problem Analysis

Mathematical Concepts

Projectile motion
Horizontal and vertical components
Kinematics

Formulas

Vertical displacement: h = 1/2 * g * t²
Horizontal velocity: vx = x / t
Vertical velocity: vy = g * t
Resultant velocity: v = sqrt(vx² + vy²)
Angle with horizontal: θ = tan⁻¹(vy / vx)

Theorems

Independence of motion components
Pythagoras' theorem

Suitable Grade Level

Grades 10-12