A student is riding the school bus. The bus stops as the driver applies the brakes. Which of these statements best describes this situation? (1 point)
A. The school bus does not lose or gain kinetic energy.
B. The bus is gaining energy because of friction.
C. There is no force acting on the bus so it stops moving.
D. A force is changing the motion of the bus.
D. A force is changing the motion of the bus.
A pitcher throws a baseball to the catcher. The ball's path begins as a straight line, and then its patch curves toward the ground. Which two forces are acting on the baseball? (1 point)
A. electricity and friction
B. gravity and friction
C. inertia and magnetism
D. nuclear and inertia
B. gravity and friction
Two people are in a rowboat on a river. The current of the river water carries them at a speed of five meters per second even when they are not rowing. What will happen to the boat's motion of no other forces act on the boat?
(1 point)
A. The boat's speed will increase.
B. The boat's speed will decrease.
C. The boat's speed will stay the same.
D. The boat will change direction.
C. The boat's speed will stay the same.
D. A force is changing the motion of the bus.
The correct answer is D. A force is changing the motion of the bus.
To understand why, let's consider the situation in more detail. When the school bus stops, the driver applies the brakes. The brakes of the bus exert a force on the wheels, causing them to slow down and eventually come to a stop. Based on Newton's laws of motion, we know that an object at rest will remain at rest unless acted upon by an external force. In this case, the force applied by the brakes is causing the bus to stop its motion.
Option A, "The school bus does not lose or gain kinetic energy," is not accurate because when the bus stops, it is losing its kinetic energy. Kinetic energy is the energy that an object possesses due to its motion, and in this case, the bus is coming to a stop, which means it is losing its motion and thus losing its kinetic energy.
Option B, "The bus is gaining energy because of friction," is incorrect as well. Friction is the force that opposes motion between two surfaces in contact. In this situation, the friction from the brakes is actually responsible for reducing the bus's energy and stopping its motion, rather than causing it to gain energy.
Option C, "There is no force acting on the bus so it stops moving," is also incorrect. As mentioned earlier, the brakes of the bus are applying a force to slow down and stop the bus's motion. Without this force, the bus would continue moving with its initial velocity.
Therefore, the most accurate statement is D. A force is changing the motion of the bus.