1
JEE Main 2019 (Online) 9th January Evening Slot
MCQ (Single Correct Answer)
+4
-1
Change Language
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
2
JEE Main 2019 (Online) 9th January Morning Slot
MCQ (Single Correct Answer)
+4
-1
Change Language
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 :
JEE Main 2019 (Online) 9th January Morning Slot Physics - Work Power & Energy Question 84 English
A
$${{2F} \over {\sqrt {mk} }}$$
B
$${F \over {\pi \sqrt {mk} }}$$
C
$${{\pi F} \over {\sqrt {mk} }}$$
D
$${F \over {\sqrt {mk} }}$$
3
JEE Main 2018 (Online) 16th April Morning Slot
MCQ (Single Correct Answer)
+4
-1
Change Language
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
4
JEE Main 2018 (Online) 16th April Morning Slot
MCQ (Single Correct Answer)
+4
-1
Change Language
Two particles of the same mass m are moving in circular orbits because of force, given by $$F\left( r \right) = {{ - 16} \over r} - {r^3}$$

The first particle is at a distance r = 1, and the second, at r = 4. The best estimate for the ratio of kinetic energies of the first and the second particle is closest to :
A
$$6 \times {10^{ - 2}}$$
B
$$3 \times {10^{ - 3}}$$
C
$${10^{ - 1}}$$
D
$$6 \times {10^{ 2}}$$
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