1
JEE Main 2019 (Online) 10th January Morning Slot
MCQ (Single Correct Answer)
+4
-1
A block of mass m is kept on a platform which starts from rest with constant acceleration g/2 upward, as shown in figure. Work done by normal reaction on block in time is -

A
$${{m{g^2}{t^2}} \over 8}$$
B
$${{3m{g^2}{t^2}} \over 8}$$
C
$$-$$ $${{m{g^2}{t^2}} \over 8}$$
D
0
2
JEE Main 2019 (Online) 9th January Evening Slot
MCQ (Single Correct Answer)
+4
-1
A force acts on a 2 kg object so that its position is given as a function of time as x = 3t2 + 5. What is the work done by this force in first 5 seconds ?
A
850 J
B
950 J
C
875 J
D
900 J
3
JEE Main 2019 (Online) 9th January Morning Slot
MCQ (Single Correct Answer)
+4
-1
A block of mass m, lying on a smooth horizontal surface, is attached to a sring (of negligible mass) of spring constant k. The other end of the spring is fixed, as shown in the figure. The block is initially at rest in its equilibrium position. If now the block is pulled with a constant force F, the maximum speed of the block is :
A
$${{2F} \over {\sqrt {mk} }}$$
B
$${F \over {\pi \sqrt {mk} }}$$
C
$${{\pi F} \over {\sqrt {mk} }}$$
D
$${F \over {\sqrt {mk} }}$$
4
JEE Main 2018 (Online) 16th April Morning Slot
MCQ (Single Correct Answer)
+4
-1
A body of mass m starts moving from rest along x-axis so that its velocity varies as $$\upsilon = a\sqrt s$$ where a is a constant and s is the distance covered by the body. The total work done by all the forces acting on the body in the first t seconds after the start of the motion is :
A
$${1 \over 8}\,$$ m a4 t2
B
8 m a4 t2
C
4 m a4 t2
D
$${1 \over 4}\,$$ m a4 t2
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