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Xavier Aptitude Test 2015 Paper
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© examsnet.com
Question : 74 of 113
Marks:
+1
,
-0
A person is standing at a distance of 1800 meters facing a giant clock at the top of a tower. At 5.00 P.M., he can see the tip of the minute hand of the clock at 30 degree elevation from his eye-level. Immediately, the person starts walking towards thetower. At 5.10 P.M., the person noticed that the tip of the minute hand made an angle of 60 degree with respect to his eye-level. Using three–dimensional vision, find the speed at which the person is walking. The length of the minutes hand is 200
√
3
meters (
√
3
= 1.732).
7.2 km/hour
7.5 km/hour
7.8 km/hour
8.4 km/hour
None of the above
Validate
Solution:
(d)
At 5:00 PM, initial distance = AB = 1800 m
Minutes hand height = CD = 200
√
3
m,
∠CAB = 30°
C
B
A
B
= tan 30° =
1
√
3
⇒CB = 600
√
3
Now, DB =
600
√
3
−
200
√
3
=
400
√
3
At 5:10 PM: the minutes hand would move from CD to
C
1
D(i.e. 60°) as follows :
D
and
D
1
are at same height.
And
∠
C
1
D
D
1
=
30
°
Now,
D
D
1
D
C
1
=
cos
30
°
⇒
D
D
1
D
C
=
√
3
2
⇒
D
D
1
200
√
3
=
√
3
2
⇒
D
D
1
=
300
m
Also
C
1
D
1
D
D
1
=
tan
30
°
⇒
C
1
D
1
300
=
1
√
3
⇒
C
1
D
1
=
100
√
3
m
At
5
:
10
P
M
,
the person moves from A to
E
, where
∠
C
1
E
B
1
=
60
°
.
Now,
C
1
B
1
=
B
1
D
1
+
D
1
C
1
=
B
D
+
D
1
C
1
⇒
C
1
B
1
=
400
√
3
+
100
√
3
=
500
√
3
m
Now,
E
B
1
C
1
B
1
=
cot
60
°
⇒
E
B
1
500
√
3
=
1
√
3
⇒
E
B
1
=
500
m
t
s
The horizontal plane EBB
1
can be presented as below:
Now,
D
D
1
=
B
B
1
=
300
m
t
s
. and
E
B
1
=
500
m
Now,
E
B
=
√
(
500
)
2
−
(
300
)
2
=
400
m
In 10 minutes, distance travelled
=
A
E
=
A
B
−
E
B
=
1800
−
400
=
1400
m
Speed
=
f
1400
×
60
10
×
1000
=
8.4
km/hr
© examsnet.com
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