1
IIT-JEE 1980
Subjective
+5
-0
(i) $$PQ$$ is a vertical tower. $$P$$ is the foot and $$Q$$ is the top of the tower. $$A, B, C$$ are three points in the horizontal plane through $$P$$. The angles of elevation of $$Q$$ from $$A$$, $$B$$, $$C$$ are equal, and each is equal to $$\theta $$. The sides of the triangle $$ABC$$ are $$a, b, c$$; and the area of the triangle $$ABC$$ is $$\Delta $$. Show that the height of the tower is $${{abc\tan \theta } \over {4\Delta }}$$.

(ii) $$AB$$ is vertical pole. The end $$A$$ is on the level ground. $$C$$ is the middle point of $$AB$$. $$P$$ is a point on the level ground. The portion $$CB$$ subtends an angle $$\beta $$ at $$P$$. If $$AP = n\,AB,$$ then show that tan$$\beta $$ $$ = {n \over {2{n^2} + 1}}$$

2
IIT-JEE 1980
Subjective
+3
-0
Give the MKS units for each of the following quantities.

(i) Young's modulus

(ii) Magnetic Induction

(iii) Power of a lens

3
IIT-JEE 1980
True or False
+1
-0
A rocket moves forward by pushing the surrounding air backwards.
A
TRUE
B
FALSE
4
IIT-JEE 1980
MCQ (Single Correct Answer)
+3
-0.75
A block of mass 2 kg rests on a rough inclined plane making an angle of $$30^\circ $$ with the horizontal. The coefficient of static friction between the block and the plane is 0.7. The frictional force on the block is
A
9.8 N
B
0.7$$ \times $$9.8$$ \times $$$$\sqrt 3 $$ N
C
9.8$$ \times $$$$\sqrt 3 $$ N
D
0.7$$ \times $$9.8
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