192

You can eliminate A & B because when the object moves through distance x, there are no forces acting along the direction of motion, i.e. no acceleration.

You eliminate D because if you change h, you change the amount of potential energy that you start out with at the top. This potential energy will be converted to kinetic energy at the bottom and will affect the speed through which the object travels distance x. Therefore, changing h does change the time required to traverse it.

C is correct because there is no net acceleration in the system during x.


193

Eliminate C and D because the force acting while the object slides down is constant (gravity). If the force is costant, acceleration is constant, it can't change.

Eliminate B because as the object slides down, potential energy is converted into kinetic energy, it must increase, not decrease.

Notice that in this question, you did not actually need to think about horizontal/vertical components.

That is the very definition of acceleration. It is change in velocity per second. so if you start at a velocity of 10 m/s, and acceleration is constant at 5 m/s^2, then after one second, the velocity is 15 m/s, and 1 second after that 20 m/s.

If acceleration is constant, then velocity must change at a constant rate.

However, the opposite cannot be true. If velocity is constant, then there cannot be a net acceleration.