Suppose that a cart is moving along a road at a constant velocity. Give two examples of ways to cause the cart to decelerate, explaining how the net force is affected.

Answer 1

To cause a cart moving at a constant velocity to decelerate, you can apply either of the following two methods:

1. Applying a Friction Force:

   • If you apply a brake or introduce friction (e.g., by dragging a rough object behind the cart or by pressing brake pads on the wheels), the friction force will act in the opposite direction to the motion of the cart.
   • This friction force provides a net force that opposes the motion of the cart, thus resulting in deceleration. According to Newton's second law (F = ma), when a net force is applied in the opposite direction of the cart's initial velocity, the acceleration will be negative (deceleration), causing the cart to slow down.

2. Inclining the Surface Downward:

   • If you change the surface on which the cart is moving to an inclined surface that tilts downward, gravity will exert a component of force along the incline, pulling the cart downward. If the incline is steep enough, this can result in a net force in the direction opposite to the cart's motion if the cart is initially moving up the incline.
   • If the cart is initially on a flat surface and you suddenly tilt the surface downward, the gravitational force acting on the cart will cause it to accelerate downward. While this might typically cause an increase in speed if the slope is downward, if the cart is already moving up the incline, the gravitational force will act against the direction of motion, producing a net force that slows the cart down.

In both examples, the application of a net force in the direction opposite to the cart's motion effectively results in deceleration, changing the velocity of the cart over time.