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Grade 11Mechanics

At t = 0 a projectile is fired from a point O(taken as origin) on the ground with a speed of 50 m/s at an angle of 53° with the horizontal. It just passes two points A & B each at height 75 m above horizontal as shown.
Q.6 The horizontal separation between the points A and B is
(A) 30 m (B) 60 m (C) 90 m (D) None
Q.7 The distance (in metres) of the particle from origin at t = 2 sec.
(A) 60√2 (B) 100 (C) 60 (D) 120

Profile image of Siddharth Sharma
10 Years agoGrade 11
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1 Answer

Profile image of Askiitians Tutor Team
ApprovedApproved Tutor Answer0 Years ago

To solve the problem of the projectile fired from the origin, we need to break down the motion into its horizontal and vertical components. Given the initial speed of 50 m/s and the launch angle of 53°, we can use some basic physics equations to find the answers to your questions about the horizontal separation between points A and B, and the distance from the origin at t = 2 seconds.

Projectile Motion Components

First, let's determine the horizontal and vertical components of the initial velocity:

  • Horizontal Component (Vx): Vx = V * cos(θ) = 50 * cos(53°)
  • Vertical Component (Vy): Vy = V * sin(θ) = 50 * sin(53°)

Calculating these values:

  • Vx = 50 * 0.6018 ≈ 30.09 m/s
  • Vy = 50 * 0.7986 ≈ 39.93 m/s

Finding Time to Reach Height of 75 m

Next, we need to find the time it takes for the projectile to reach a height of 75 m. We can use the vertical motion equation:

y = Vy * t - (1/2) * g * t²

Where g is the acceleration due to gravity (approximately 9.81 m/s²). Setting y = 75 m, we have:

75 = 39.93 * t - (1/2) * 9.81 * t²

This simplifies to:

0 = -4.905t² + 39.93t - 75

Using the quadratic formula, t = [−b ± √(b² - 4ac)] / 2a, where a = -4.905, b = 39.93, and c = -75:

Calculating the discriminant:

b² - 4ac = (39.93)² - 4 * (-4.905) * (-75) ≈ 1595.6049 - 1477.5 = 118.1049

Now, substituting into the quadratic formula:

t = [−39.93 ± √(118.1049)] / (2 * -4.905)

Calculating the two possible times:

t₁ ≈ 8.96 seconds and t₂ ≈ 1.67 seconds (the time to reach the height on the way up and down).

Horizontal Separation Between Points A and B

Now, we can find the horizontal distance traveled during these times:

Horizontal Distance (d) = Vx * t

For t₁ (upward path):

d₁ = 30.09 * 1.67 ≈ 50.23 m

For t₂ (downward path):

d₂ = 30.09 * 8.96 ≈ 269.45 m

The horizontal separation between points A and B is:

Horizontal Separation = d₂ - d₁ ≈ 269.45 - 50.23 ≈ 219.22 m

However, since we are looking for the separation between the two points at the same height, we only consider the time it takes to reach 75 m on the way up and down, which gives us a total horizontal distance of:

Horizontal Separation = 30.09 * (t₁ + t₂) ≈ 30.09 * (1.67 + 1.67) ≈ 30.09 * 3.34 ≈ 100.4 m.

Since this does not match any of the options provided, we conclude that the answer is (D) None.

Distance from Origin at t = 2 seconds

Now, let’s find the distance of the particle from the origin at t = 2 seconds. We can use the following formulas:

Horizontal Distance (x) = Vx * t

Vertical Distance (y) = Vy * t - (1/2) * g * t²

Calculating x:

x = 30.09 * 2 ≈ 60.18 m

Calculating y:

y = 39.93 * 2 - (1/2) * 9.81 * (2)² ≈ 79.86 - 19.62 ≈ 60.24 m

Now, we can find the resultant distance from the origin using the Pythagorean theorem:

Distance = √(x² + y²)

Distance = √((60.18)² + (60.24)²) ≈ √(3621.6324 + 3628.0576) ≈ √7249.69 ≈ 85.1 m.

Since this also does not match the provided options, we conclude that the answer is (D) None for the distance from the origin at t = 2 seconds as well.