To cause the cart to decelerate, you can change the forces acting on it in such a way that the net force acting on the cart is in the opposite direction to its motion. Here are two examples:
Example 1: Applying the Brakes
When a driver applies the brakes of the cart, friction between the brake pads and the wheels creates a force that opposes the motion of the cart. This braking force reduces the cart's speed.
- How Net Force is Affected: The force of friction (braking force) acts in the opposite direction of the cart's velocity. If the initial motion of the cart is in the positive direction (e.g., moving to the right), the braking force will act to the left. According to Newton's second law (F = ma), since there is a net force acting in the direction opposite to the motion, the acceleration (in this case, deceleration) will be negative, causing the cart to slow down.
Example 2: Increasing Air Resistance
If the cart's speed increases (for example, if the driver accelerates), something like deploying a parachute or an air brake can be used to increase air resistance. This added drag force opposes the forward motion of the cart.
- How Net Force is Affected: When air resistance is increased, the drag force acting in the opposite direction of the cart's motion becomes greater than the driving force propelling the cart forward. Thus, as the drag force increases, the net force acting on the cart becomes negative (opposite to its direction of motion), resulting in a reduction of the cart's velocity. In this case, the net force leads to a deceleration of the cart.
In both examples, the key factor is that an external force is acting against the motion of the cart, resulting in a net force that causes the cart to lose speed.
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