3D colliders in Unity - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this OnCollisionEnter method?

Consider a Unity script attached to a GameObject with a BoxCollider and Rigidbody. What will be printed when this object collides with another?

Unity

void OnCollisionEnter(Collision collision) {
    Debug.Log($"Collided with {collision.gameObject.name}");
}

A Error: collision is null

B Collided with null

C No output, method not called

D Collided with Player

💡 Hint

OnCollisionEnter is called only when both objects have colliders and at least one has a Rigidbody.

The method prints the name of the other GameObject involved in the collision. If the other object is named 'Player', it prints 'Collided with Player'.

🧠 Conceptual

intermediate

Which collider type allows trigger events but does not physically block objects?

In Unity 3D, which collider type lets objects pass through but still detects overlaps for events?

A MeshCollider with convex set to false

B BoxCollider with isTrigger set to true

C SphereCollider with isTrigger set to false

D CapsuleCollider with isTrigger set to false

💡 Hint

Triggers detect overlaps but do not cause physical collisions.

Setting isTrigger to true on any collider makes it a trigger collider, which detects overlaps but does not block movement.

🔧 Debug

advanced

Why does this OnTriggerEnter method never get called?

Given this script on a GameObject with a SphereCollider set as trigger, why is OnTriggerEnter not called when another object enters?

Unity

void OnTriggerEnter(Collider other) {
    Debug.Log("Trigger entered by " + other.gameObject.name);
}

A The other object does not have a Rigidbody component

B The SphereCollider is not set as trigger

C The script is not attached to any GameObject

D The method signature is incorrect

💡 Hint

Triggers require at least one Rigidbody involved in the collision.

OnTriggerEnter is called only if one of the colliding objects has a Rigidbody. Without Rigidbody on the other object, the event won't fire.

📝 Syntax

advanced

Which option correctly defines a MeshCollider as convex in C#?

Choose the correct syntax to set a MeshCollider's convex property to true in a Unity script.

Unity

MeshCollider meshCollider = gameObject.GetComponent<MeshCollider>();

A meshCollider.Convex = true;

B meshCollider.setConvex(true);

C meshCollider.convex = true;

D meshCollider.convex(true);

💡 Hint

Properties in C# are accessed without parentheses.

The convex property is a boolean property accessed directly with lowercase 'convex'. Methods like setConvex do not exist.

🚀 Application

expert

How many colliders are active after this code runs?

Given a GameObject with 1 BoxCollider and 1 SphereCollider, this code disables the BoxCollider and adds a CapsuleCollider. How many colliders are active?

Unity

BoxCollider box = gameObject.GetComponent<BoxCollider>();
box.enabled = false;
CapsuleCollider capsule = gameObject.AddComponent<CapsuleCollider>();

A 2

B 0

C 3

D 1

💡 Hint

Disabling a collider stops it from being active but does not remove it.

The BoxCollider is disabled (not active), the SphereCollider remains active, and the new CapsuleCollider is active. So total active colliders: 2.