Velocity making weird things

Hi, im trying to simulate a bullet being fired at a 45° degree angle but as soon as my world makes the first step the Velocity bombs from 668 m/s to 84 m/s, this is the code:

#include <Box2D/Box2D.h>
#include <iostream>
#include <cmath>

#ifndef M_PI
#define M_PI 3.14159265358979323846
#endif

int main() {
    // Define the gravity vector
    b2Vec2 gravity(0.0f, -9.81f);

    // Construct a world object, which will hold and simulate the rigid bodies
    b2World world(gravity);

    // Create a dynamic body for the bullet
    b2BodyDef bodyDef;
    bodyDef.type = b2_dynamicBody;
    bodyDef.position.Set(0.0f, 0.0f);
    b2Body* body = world.CreateBody(&bodyDef);
[box2d_dump.txt](https://github.com/erincatto/box2d/files/12721822/box2d_dump.txt)

    // Define another box shape for the bullet
    b2PolygonShape dynamicBox;
    dynamicBox.SetAsBox(0.06f, 0.019f);

    // Define the dynamic body fixture
    b2FixtureDef fixtureDef;
    fixtureDef.shape = &dynamicBox;
    fixtureDef.density = 0.0f;
    fixtureDef.friction = 0.0f;

    // Add the shape to the body
    body->CreateFixture(&fixtureDef);

    // Create a mass data object to hold the mass of the bullet
    b2MassData massData;
    massData.mass = 0.0650f;
    massData.center = body->GetPosition();
    massData.I = 0.1f;
    body->SetMassData(&massData);
    float mass = massData.mass;

    // Set the initial velocity of the bullet
    float angle = 45.0f; // Angle in degrees
    float rad_angle= angle * (M_PI) / 180.0f ; // Convert an angle to radians
    float speed = 945.0f; // Speed in m/s
    float vx = speed * std::cos(rad_angle);
    float vy = speed * std::sin(rad_angle);
    b2Vec2 prevVelocity(vx, vy);

    body->SetLinearVelocity(prevVelocity);
    body->SetLinearDamping(0.15f);
    std::cout << prevVelocity.x << " " << prevVelocity.y << std::endl;

    // Simulate the world
    float timeStep = 1.0f / 60.0f;
    int32 velocityIterations = 8;
    int32 positionIterations = 8;

    for (int i = 0; i < 60; ++i)
    {
        body->SetLinearVelocity(prevVelocity);
        world.Step(timeStep, velocityIterations, positionIterations);

        // Calculate the kinetic energy of the bullet
        b2Vec2 currentVelocity = body->GetLinearVelocity();
        float linearVelocity = (currentVelocity.x * currentVelocity.x) + (currentVelocity.y * currentVelocity.y);
        linearVelocity = sqrt(linearVelocity);
        float kineticEnergy = 0.5f *(mass * (linearVelocity * linearVelocity));

        std::cout << "Bullet Position: (" << body->GetPosition().x << "," << body->GetPosition().y << ")" << std::endl;
        std::cout << "Bullet Velocity: (" << linearVelocity << ")"<< std::endl;
        std::cout << "Kinetic energy of bullet: " << kineticEnergy <<" " << "Joules" << std::endl;

        prevVelocity = currentVelocity;
    }

    // Remember to clean up
    world.DestroyBody(body);

    return 0;
}

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[x] Consider providing a dump file using b2World::Dump

erincatto / box2d

Velocity making weird things #755