Published by:
CGP EDU Academic Team
Published on: September 12, 2026
A player kicks a football at an angle of 45º with an initial speed of 20 m/s. A second player on the goal line 60 m away in the direction of kick starts running to receive the ball at that instant. Find the speed of the second player with which he should run to catch the ball before it hits the ground. [g = 10 m/s 2 ]
Text Solution
Verified by ExpertsThe correct answer is:
B
Step 1: Resolve the initial velocity into its components.
The initial speed of the football is given as 20 m/s and the angle of projection is 45º.
The horizontal component of the velocity (Vx) is:
$$V_x = V imes ext{cos}( heta) = 20 imes ext{cos}(45º) = 20 imes \frac{1}{\sqrt{2}} = 10\sqrt{2} ext{ m/s}$$
The vertical component of the velocity (Vy) is:
$$V_y = V imes ext{sin}( heta) = 20 imes ext{sin}(45º) = 20 imes \frac{1}{\sqrt{2}} = 10\sqrt{2} ext{ m/s}$$
Step 2: Calculate the time of flight (T).
The time of flight for projectile motion is given by the formula:
$$T = \frac{2V_y}{g}$$
Substituting the values:
$$T = \frac{2 \times 10\sqrt{2}}{10} = 2\sqrt{2} ext{ seconds}$$
Step 3: Calculate the horizontal distance traveled by the ball.
Using the horizontal component of the velocity, the horizontal distance (D) covered by the ball is:
$$D = V_x \times T = (10\sqrt{2}) \times (2\sqrt{2}) = 20 ext{ meters}$$
Step 4: Calculate the distance the player needs to run.
The player is initially 60 m away, and the ball covers 20 m horizontally. Thus, the distance the player needs to run is:
$$60 - 20 = 40 ext{ meters}$$
Step 5: Calculate the speed of the player (Vp).
The speed of the player can be calculated as:
$$V_p = \frac{ ext{Distance}}{T} = \frac{40}{2\sqrt{2}} = \frac{20}{\sqrt{2}} = 10\sqrt{2} ext{ m/s}$$
Therefore, the speed of the second player with which he should run to catch the ball is approximately 14.14 m/s. Hence, the answer is option B.
The initial speed of the football is given as 20 m/s and the angle of projection is 45º.
The horizontal component of the velocity (Vx) is:
$$V_x = V imes ext{cos}( heta) = 20 imes ext{cos}(45º) = 20 imes \frac{1}{\sqrt{2}} = 10\sqrt{2} ext{ m/s}$$
The vertical component of the velocity (Vy) is:
$$V_y = V imes ext{sin}( heta) = 20 imes ext{sin}(45º) = 20 imes \frac{1}{\sqrt{2}} = 10\sqrt{2} ext{ m/s}$$
Step 2: Calculate the time of flight (T).
The time of flight for projectile motion is given by the formula:
$$T = \frac{2V_y}{g}$$
Substituting the values:
$$T = \frac{2 \times 10\sqrt{2}}{10} = 2\sqrt{2} ext{ seconds}$$
Step 3: Calculate the horizontal distance traveled by the ball.
Using the horizontal component of the velocity, the horizontal distance (D) covered by the ball is:
$$D = V_x \times T = (10\sqrt{2}) \times (2\sqrt{2}) = 20 ext{ meters}$$
Step 4: Calculate the distance the player needs to run.
The player is initially 60 m away, and the ball covers 20 m horizontally. Thus, the distance the player needs to run is:
$$60 - 20 = 40 ext{ meters}$$
Step 5: Calculate the speed of the player (Vp).
The speed of the player can be calculated as:
$$V_p = \frac{ ext{Distance}}{T} = \frac{40}{2\sqrt{2}} = \frac{20}{\sqrt{2}} = 10\sqrt{2} ext{ m/s}$$
Therefore, the speed of the second player with which he should run to catch the ball is approximately 14.14 m/s. Hence, the answer is option B.
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