She threw the marshmallow at a speed of around 4.76 m/s.The formula for the horizontal range gives the velocity.
<h3>What is projectile motion?</h3>The motion of an item hurled or projected into the air, subject only to gravity's acceleration, is known as projectile motion.
The item is known as a projectile, and the course it takes is known as a trajectory. Falling object motion is a simple one-dimensional kind of projectile motion with no horizontal movement.
Given data;
The marshmallow was thrown at a distance of 2 meters
Range,R = 3 m
Initial velocity,u
The angle at which the marshmallow was thrown,θ = 30°
The acceleration due to gravity,g = 9.81 m/s²
The projectile's motion is divided into two parts: horizontal and vertical motion.
Hence, she throws the marshmallow at a speed of 4.76 m/sec.
To learn more about the projectile motion refer to the link;
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