FORCES REVIEW

Try this problem:

A
30 kg block sits on a ramp that is 2 meters long at a

45
degree angle. It slides down the ramp with NO friction.

Then
it slides along the rough floor

and
stops after 10 meters.

What
is the coefficient of friction

between
the block and the floor?

FIRST:

2 parts: ramp and floor

Ramp:

Mass
of block=30 kg

Weight
of block=W=mg=30*9.8=294 N

Parallel
force down ramp=Wsin =294*sin45=207.89 N

Acceleration=
Fnet=Fparallel=207.89=mA, 207.89=30*A, A= 207.89/30=6.93 m/s2

Distance=
2

Initial
velocity=0

Final
velocity= sqrt (2*A*D)= sqrt (2*6.93*2)=5,26 m/s

Floor:

Initial
velocity= 5.26 m/s

Final
velocity= 0

Weight
of block= 294 N

Normal
force= 294 N

Distance=
10 m

Deacceleration=
Vi^{2}/2D = 5.26^{2}/(2*10) =-1.386 m/s^{2}

Force
friction=Fnet=mA=30*1.389=41.6 N=uFn =u (294)

Coefficient
of friction= 41.6/294=.14

For
test:

What
factors affect the force of air resistance? Surface are, Mass, velocity, air
properties

What
is terminal velocity and what does it depend on? When air res = force of
gravity

Describe
the path of a brick thrown at an angle of 45degrees into the air with air
resistance that then lands and skids on the ground.

Describe
how to draw a force diagram for moving objects.

Describe
the relationship between mass, weight, and acceleration due to gravity.

If
an object is moving at a constant speed describe the forces acting on it. Fnet
= 0

How
are the properties of static and starting friction related?

Explain,
using Newton’s 2^{nd} law, why giving with a baseball pitch hurts your
hand less. More t, less a, so less F F=ma=m*v/t

Describe
Newton’s 1^{st} law.

Describe
the forces, motion, and acceleration of two objects pushing each other, and
what it depends on.

Describe
the four fundamental forces, their range, strength, and how we perceive them in
everyday life. Gravity, em, strong, weak

Describe
how scientists study fundamental forces.

Describe
the normal force and how to calculate it. Fn = force push back, usually weight

Describe
how to calculate the coefficient of friction. =Ff/FN

Describe
how to calculate the acceleration of
an object moving horizontally with friction, a push, and gravity acting
on it. Fnet=ma so a =Fnet/m
Fnet=Fp-Ff, Ff=u FN, FN=W=mg

Describe
how to calculate the coefficient of friction of an object moving at a constant
speed down a ramp. Tan angle

Explain
why the coeeficient of friction does NOT depend on the mass or surface area of
an object.