Motion and Force - Some questions after doing revision.

[yutou.eu]

I am having assessment test for this chapter tomorrow, I have some questions after doing this whole chapter questions. Hope you guys can help me :)

1. A brick of mass 3.2Kg on a sloping flat roof, at 30 degree to the horizontal, slides at constant acceleration 2.0m down the roof in 2.0 s from rest Calculate:

a. the acceleration of the brick.
> hmm. a = (v-u)/t..? F = ma so a = F/m..? or mgsin(delta) - F0 = ma?

b. the frictional force on the brick due to the roof.
friction force mean the force is pulling upward isn't it? so is it the same F=ma?

2. Wheather or not a smaller steel ball would fall at the same rate in the same liquid?
Edited: I have found that will be the same rate no matter how heavy the object is, but is it the same in the liquid?

3. Why a cyclist can reach a higher top speed by crouching over the handlebars instead of sitting upright while pedalling?

4. Why a vehicle has a higher top speed on a downhill stretch of road than on a level road?

5. What is meant by the bracking distance of a vehicle?
>Braking distance refers to the distance a vehicle will travel from the point where its brakes are fully applied to when it comes to a complete stop. From Wikipedia.

6. Explain in terms of the forces acting on the wheels of a car, why a vehicle slows down when the brakes are applied.

 

[jbsteele]

>The brakes produce a force that acts in the opposite direction of the motion of the vehicle, reducing its speed. This force is known as the braking force, and it acts on the wheels of the car, causing them to turn more slowly. The friction between the tires and the road also helps to slow down the car by providing an opposing force to the movement of the wheels.