Mechanical Engineering - Automobile Engineering - Discussion
Discussion Forum : Automobile Engineering - Section 2 (Q.No. 8)
8.
The air resistance to a car at 20 kmph is R. The air resistance at 40 kmph will be
Discussion:
7 comments Page 1 of 1.
Dhruvil said:
4 years ago
F is directly proportional to v^(3/2)
F= (1/2) (rho) (v^2) (Area) (skin friction coeff).
now, Skin fric coeff= 1.328/ (reynold num.)^(1/2),
and Reynold num = Rho*v*L/mu.
Now putting the value of skin friction Coeff and Reynold number in the main equation.
F= (v^2)/ (v^(1/2)),
F= k. V^(3/2).
So, the correct answer is 2.828R.
F= (1/2) (rho) (v^2) (Area) (skin friction coeff).
now, Skin fric coeff= 1.328/ (reynold num.)^(1/2),
and Reynold num = Rho*v*L/mu.
Now putting the value of skin friction Coeff and Reynold number in the main equation.
F= (v^2)/ (v^(1/2)),
F= k. V^(3/2).
So, the correct answer is 2.828R.
(1)
Anindam said:
4 years ago
@Nikunj_Patel.
How? Explain please.
How? Explain please.
Nikunj Patel said:
5 years ago
20kmph R resistance.
30kmph. 2R resistance.
40 kmph 4R resistance.
50 kmph 8R resistance.
30kmph. 2R resistance.
40 kmph 4R resistance.
50 kmph 8R resistance.
Roshan Thakkar said:
5 years ago
The air resistance to a car at 20 kmph is R.
Multiply by 2 at both side,
20 = R.
20*2 = 2*R.
40 = 2R.
Multiply by 2 at both side,
20 = R.
20*2 = 2*R.
40 = 2R.
Ajeya said:
8 years ago
Can anyone tell me, any reference book for this problem?
Sibikrishna said:
9 years ago
Air Resistance Formula,
F = c x v^2.
For 20 Kmph, Given: F = R & v = 20 Kmph.
R = c x 400.
c = R/400.
For 40 kmph,
F = c x v^2.
F = (R/400) x 1600.
F = 4R.
F = c x v^2.
For 20 Kmph, Given: F = R & v = 20 Kmph.
R = c x 400.
c = R/400.
For 40 kmph,
F = c x v^2.
F = (R/400) x 1600.
F = 4R.
(1)
DUGGU RATHORE said:
1 decade ago
R = K.A.V2 when vehicle speed is about 20km/hr.
Where K = Co-efficient of air resistance.
A = Projected area of vehicle.
V = Vehicle speed in km/hr.
When vehicle speed is about 40km/hr, speed is doubled so we can write V=2V,
Therefore, R = K.A.(2V)2.
R = K.A.4V2.
R = 4K.A.V2.
R= 4R (where, R = K.A.V2)
Where K = Co-efficient of air resistance.
A = Projected area of vehicle.
V = Vehicle speed in km/hr.
When vehicle speed is about 40km/hr, speed is doubled so we can write V=2V,
Therefore, R = K.A.(2V)2.
R = K.A.4V2.
R = 4K.A.V2.
R= 4R (where, R = K.A.V2)
(2)
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