Rigidbody 3D component in Unity - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Rigidbody velocity code?

Consider this Unity C# script snippet attached to a GameObject with a Rigidbody component:

void Start() {
    Rigidbody rb = GetComponent();
    rb.velocity = new Vector3(0, 10, 0);
    Debug.Log(rb.velocity.y);
}

What will be printed in the console when the game starts?

Unity

void Start() {
    Rigidbody rb = GetComponent<Rigidbody>();
    rb.velocity = new Vector3(0, 10, 0);
    Debug.Log(rb.velocity.y);
}

A NullReferenceException

B Vector3(0, 10, 0)

C 10

D 0

💡 Hint

Remember that rb.velocity is a Vector3 representing speed in each direction.

The velocity is set to (0, 10, 0), so rb.velocity.y is 10, which is printed.

🧠 Conceptual

intermediate

Which Rigidbody property controls if gravity affects the object?

In Unity's Rigidbody 3D component, which property determines whether the object is affected by gravity?

A drag

B isKinematic

C mass

D useGravity

💡 Hint

Think about the property that toggles gravity on or off.

The useGravity property enables or disables gravity's effect on the Rigidbody.

🔧 Debug

advanced

Why does this Rigidbody not move when force is applied?

Look at this code snippet:

void Start() {
    Rigidbody rb = GetComponent();
    rb.isKinematic = true;
    rb.AddForce(new Vector3(0, 500, 0));
}

Why does the Rigidbody not move when the game runs?

A Because <code>isKinematic</code> is true, physics forces are ignored

B Because the force vector is too small to move the object

C Because <code>AddForce</code> must be called in Update, not Start

D Because the Rigidbody component is missing

💡 Hint

Check what isKinematic does to Rigidbody behavior.

When isKinematic is true, the Rigidbody ignores physics forces like AddForce.

📝 Syntax

advanced

Which code correctly applies an impulse force to a Rigidbody?

Choose the correct C# code snippet to apply an impulse force upwards to a Rigidbody named rb:

A rb.AddForce(new Vector3(0, 10, 0), ForceMode.Impulse);

B rb.AddForce(new Vector3(0, 10, 0), ForceMode.Force);

C rb.AddForce(new Vector3(0, 10, 0));

D rb.AddImpulse(new Vector3(0, 10, 0));

💡 Hint

Impulse force applies an instant push. Check the ForceMode enum.

AddForce with ForceMode.Impulse applies an instant force. Option A uses default ForceMode.Force which is continuous. Option A is invalid method.

🚀 Application

expert

How many Rigidbody components are active after this code runs?

Given a GameObject with two Rigidbody components attached (which is unusual but possible), and this code runs:

void Start() {
    Rigidbody[] rbs = GetComponents();
    foreach (var rb in rbs) {
        rb.isKinematic = true;
    }
    rbs[0].isKinematic = false;
}

How many Rigidbody components will be affected by physics (not kinematic) after Start?

A 0

B 1

C 2

D Cannot have two Rigidbody components on one GameObject

💡 Hint

Think about how the loop sets all to kinematic, then one is set back.

Initially both are set to kinematic (no physics). Then the first Rigidbody is set to non-kinematic, so only one Rigidbody is affected by physics.