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jee king king Grade: 12
        1.the no of integral solutions of equation 4[Integral 0 to infinity(ln tdt/x2 +t2) –Pi ln2=0,x>0 is

A) 0 B) 1 C) 2 D) 3

2. If integral 2 to 1 (ax2-5)dx = 0 and 5 + integral 1 to 2 (bx+c) dx = 0 then

A) ax2-bx+c = 0 has atleast one root in (1,2)
B) ax2-bx+c = 0 has atleast one root in (-2 ,-1)
C) ax2 + bx+c = 0 has atleast one root in (-2,-1)
D)none of these

3. A block of mass m slides down an inclined wedge of same mass m shown in the figure.Friction is absent every where. Magnitude of acceleration of centre of mass of the block and the wedge is

A) 0
B) gsin2 (theta)/(1+ sin2 (theta))
C) gcos2 (theta)/(1+ sin2 (theta))
D) gcos (theta)/(1+ cos (theta))






Please send detailed solutions.
7 years ago

Answers : (1)

Jitender Singh
IIT Delhi
askIITians Faculty
158 Points
										
Ans:
1.
I = \int_{0}^{\infty }\frac{ln(t)}{x^{2}+t^{2}}dt
x = 0
Integral is divergent.
x = \pm 1
I = \int_{0}^{\infty }\frac{ln(t)}{1+t^{2}}dt
I = 0
x = \pm 2
I = \int_{0}^{\infty }\frac{ln(t)}{2^{2}+t^{2}}dt
I = \frac{\pi }{4}ln2
Since x > 0
There is only one integral solution (x = 2).
2.
\int_{2}^{1}(ax^{2}-5)dx = 0
(a\frac{x^{3}}{3}-5x)_{2}^{1} = 0
a(\frac{1}{3}-\frac{8}{3})-5(1-2) = 0
\frac{-7a}{3}+5 = 0
\Rightarrow a = \frac{15}{7}
5 + \int_{1}^{2}(bx+c)dx = 0
5 + (\frac{bx^{2}}{2}+cx)_{1}^{2}= 0
5 + \frac{3b}{2}+c = 0
3b + 2c = -10
Apply the rolle’s theorm & you will get the answer.
3.Diagram is not given.
Thanks & Regards
Jitender Singh
IIT Delhi
askIITians Faculty
3 years ago
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