Vcoderz Community - physics problems

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physics problems

hello guys long time :)
plz i need help in 2 physics problems...most of u are at uni now and still have some fresh memory...these problems r about work-kinetic energy theorem....i have the final answers bt i cant reach them... any help is appreciated:
Question 1:
A 2100 kg car starts from rest at the top pf a driveway that is sloped at an angle of 20 degrees wit the horizontal. An average friction force of 4000N impedes the car's motion so that the car's speed at the bottom of the driveway is 3.8m/s . What is the length of the driveway?

Question 2:
A 10 kg crate is pulled up a rough incline with an initial speed of 1.5m/s. The pulling force is 100N parallel to the incline, which makes an angle of 15 degrees with the horizontal. Assuming the coefficient of kinetic friction is 0.4 and the crate is pulled a distance of 7.5m, find the following:
a. the work done by the Earth's gravity on the crate
b. the work done by the force of friction on the crate
c. the work done by the puller on the crate
d. the change in kinetic energy of the crate
e. the speed of the crate after it is pulled 7.5 m

thank u in advance

Q1 :
net force on the car F = m g sin(20) - f = 2100 x9.8 x0.342 - 4000 = 3038 N
and so, aceleration of car a = F / m = 3038 /2100 = 1.45 m/sec^2

then, if L is the length of the drive way, using the relation V^2 - 0 = 2 a L, we have

L = V^2 / 2 a = 3.8 x3.8 / 2 x1.45 = 5 m ( nearly )

Q2:
The forces acting are:
The pulling force 100N parallel to the plane;
Weight of the crate = 10 * 9.81 N vertically down;
Normal reaction of the plane = 10 * 0.4 * 9.81 cos(15) N;
Friction = 0.4 * 10 * 9.81 cos(15) N down and parallel to the plane.
The vertical rise in 7.5 sin(15) m.

(a)
- 10 * 9.81 * 7.5 sin(a) = - 190.4 J.

(b)
- 0.4 * 10 * 9.81 * 7.5 = - 294.3 J.

(c) 100 * 7.5 = 750 J.

(d)
750 - 294.3 - 190.4 = 265.3 N.

(e)
If v is the final speed:
10(v^2 - 1.5^2) / 2 = 265.3
v^2 = (2 * 265.3) / 10 + 1.5^2
v = 7.44 m/s.

i knew i should have went to engineering school (H)

One day u asked me about the root cube of 27 !:p how come u solved this?(its not that hard)but u stunned me, I'm impressed :p you should've said "Bazinga!" at the end lool

A wise member once said:

Quote:

Systamatics, cause he's like VcoderZ' Element of Surprise.

dude , google is my head lool .
maybe i should have kept silent and pretended to be smart :p

Quote:

Originally Posted by SysTaMatIcS (Post 210038)

dude , google is my head

Really Google??????????