1
AIPMT 2009
MCQ (Single Correct Answer)
+4
-1
If $$\overrightarrow F $$ is the force acting on a particle having position vector $$\overrightarrow r $$ and $$\overrightarrow \tau $$ be the torque of this force about the origin, then
A
$$\overrightarrow r .\overrightarrow \tau > 0$$  and  $$\overrightarrow F .\overrightarrow \tau < 0$$
B
$$\overrightarrow r .\overrightarrow \tau = 0$$  and  $$\overrightarrow F .\overrightarrow \tau = 0$$
C
$$\overrightarrow r .\overrightarrow \tau = 0$$  and  $$\overrightarrow F .\overrightarrow \tau \ne 0$$
D
$$\vec r.\vec \tau \ne 0$$  and  $$\overrightarrow F .\overrightarrow \tau = 0$$
2
AIPMT 2009
MCQ (Single Correct Answer)
+4
-1
Two bodies of mass 1 kg and 3 kg have position vectors $$\widehat i + 2\widehat j + \widehat k$$ and $$ - 3\widehat i - 2\widehat j + \widehat k$$, respectively. The center of mass of this system has a position vector :
A
$$ - 2\widehat i - \widehat j + \widehat k$$
B
$$2\widehat i - \widehat j - 2\widehat k$$
C
$$ - \widehat i + \widehat j + \widehat k$$
D
$$ - 2\widehat i + 2\widehat k$$
3
AIPMT 2009
MCQ (Single Correct Answer)
+4
-1
A black body at 227oC radiates heat at the rate of 7 cals/cm2s. At a temperature of 727oC, the rate of heat radiated in the same units will be
A
50
B
112
C
80
D
60
4
AIPMT 2009
MCQ (Single Correct Answer)
+4
-1
The two ends of a rod of length L and a uniform cross-sectional area A are Kept at two temperatures T1 and T2 (T1 > T2). The rate of heat transfer, $${{dQ} \over {dt}}$$ through the rod in a steady state is given by :
A
$${{dQ} \over {dt}} = {{k\left( {{T_1} - {T_2}} \right)} \over {LA}}$$
B
$${{dQ} \over {dt}} = kLA({T_1} - {T_2})$$
C
$${{dQ} \over {dt}} = {{kA\left( {{T_1} - {T_2}} \right)} \over L}$$
D
$${{dQ} \over {dt}} = {{kL\left( {{T_1} - {T_2}} \right)} \over A}$$
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