Collider2D types (box, circle, polygon) in Unity - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Collider2D Type Check

What will be printed by this Unity C# script when attached to a GameObject with a CircleCollider2D?

using UnityEngine;

public class ColliderTypeCheck : MonoBehaviour {
    void Start() {
        Collider2D col = GetComponent();
        if (col is BoxCollider2D) {
            Debug.Log("Box Collider");
        } else if (col is CircleCollider2D) {
            Debug.Log("Circle Collider");
        } else if (col is PolygonCollider2D) {
            Debug.Log("Polygon Collider");
        } else {
            Debug.Log("Unknown Collider");
        }
    }
}

Unity

using UnityEngine;

public class ColliderTypeCheck : MonoBehaviour {
    void Start() {
        Collider2D col = GetComponent<Collider2D>();
        if (col is BoxCollider2D) {
            Debug.Log("Box Collider");
        } else if (col is CircleCollider2D) {
            Debug.Log("Circle Collider");
        } else if (col is PolygonCollider2D) {
            Debug.Log("Polygon Collider");
        } else {
            Debug.Log("Unknown Collider");
        }
    }
}

A Unknown Collider

B Box Collider

C Circle Collider

D Polygon Collider

💡 Hint

Think about which collider type is attached to the GameObject.

The script checks the type of the Collider2D component. Since the GameObject has a CircleCollider2D, it prints "Circle Collider".

❓ Predict Output

intermediate

PolygonCollider2D Points Count

What is the output of this code snippet when the PolygonCollider2D has 3 points defined?

using UnityEngine;

public class PolygonPointsCount : MonoBehaviour {
    void Start() {
        PolygonCollider2D poly = GetComponent();
        Debug.Log(poly.GetPath(0).Length);
    }
}

Unity

using UnityEngine;

public class PolygonPointsCount : MonoBehaviour {
    void Start() {
        PolygonCollider2D poly = GetComponent<PolygonCollider2D>();
        Debug.Log(poly.GetPath(0).Length);
    }
}

A 3

B 0

C 1

D Throws NullReferenceException

💡 Hint

GetPath(0) returns the first path's points array.

The PolygonCollider2D has 3 points in its first path, so GetPath(0).Length returns 3.

🔧 Debug

advanced

Why does this BoxCollider2D size not update?

Consider this code snippet attached to a GameObject. The size does not update as expected. What is the cause?

using UnityEngine;

public class BoxSizeChanger : MonoBehaviour {
    void Start() {
        BoxCollider2D box = GetComponent();
        box.size = new Vector2(5, 5);
    }
}

Unity

using UnityEngine;

public class BoxSizeChanger : MonoBehaviour {
    void Start() {
        BoxCollider2D box = GetComponent<BoxCollider2D>();
        box.size = new Vector2(5, 5);
    }
}

A The size property is read-only and cannot be changed at runtime.

B The BoxCollider2D component is missing from the GameObject.

C The BoxCollider2D size is overridden by the attached Rigidbody2D component.

D The code runs in Start(), but another script resets the size later.

💡 Hint

Check if the component exists before changing its properties.

If the BoxCollider2D component is missing, GetComponent returns null, so setting size throws NullReferenceException.

📝 Syntax

advanced

Identify the syntax error in CircleCollider2D assignment

Which option contains the correct syntax to assign a radius of 3.5 to a CircleCollider2D component in Unity C#?

A circleCollider.radius := 3.5f;

B circleCollider.radius == 3.5f;

C circleCollider.radius = 3.5;

D circleCollider.radius = 3.5f;

💡 Hint

Remember the assignment operator in C#.

Option D uses the correct assignment operator '=' and the float literal '3.5f'. Option D uses '==' which is a comparison, C uses a double literal without 'f', and A uses invalid ':=' operator.

🚀 Application

expert

Calculate total area covered by multiple Collider2D types

You have a GameObject with three Collider2D components: a BoxCollider2D of size (2,3), a CircleCollider2D of radius 1, and a PolygonCollider2D with a triangle path of points (0,0), (1,0), (0,1). Which code snippet correctly calculates the total approximate area covered by all three colliders?

A float totalArea = 2 * 3 + Mathf.PI * 1 * 1 + 0.5f * 1 * 1;

B float totalArea = 2 + 3 + Mathf.PI * 1 + 1.5f;

C float totalArea = (2 + 3) * Mathf.PI * 1 * 1 * 0.5f * 1 * 1;

D float totalArea = Mathf.PI * 2 * 3 + 1 + 0.5f;

💡 Hint

Recall formulas for rectangle, circle, and triangle areas.

The BoxCollider2D area is width * height = 2 * 3 = 6. The CircleCollider2D area is π * r² = π * 1² = π. The triangle area is 0.5 * base * height = 0.5 * 1 * 1 = 0.5. Summing these gives 6 + π + 0.5.