1
JEE Main 2021 (Online) 1st September Evening Shift
+4
-1
A body of mass 'm' dropped from a height 'h' reaches the ground with a speed of 0.8$$\sqrt {gh}$$. The value of workdone by the air-friction is :
A
$$-$$0.68 mgh
B
mgh
C
1.64 mgh
D
0.64 mgh
2
JEE Main 2021 (Online) 31st August Evening Shift
+4
-1
A block moving horizontally on a smooth surface with a speed of 40 m/s splits into two parts with masses in the ratio of 1 : 2. If the smaller part moves at 60 m/s in the same direction, then the fractional change in kinetic energy is :-
A
$${{1 \over 3}}$$
B
$${{2 \over 3}}$$
C
$${{1 \over 8}}$$
D
$${{1 \over 4}}$$
3
JEE Main 2021 (Online) 27th July Evening Shift
+4
-1
Given below is the plot of a potential energy function U(x) for a system, in which a particle is in one dimensional motion, while a conservative force F(x) acts on it. Suppose that Emech = 8 J, the incorrect statement for this system is :

[ where K.E. = kinetic energy ]
A
at x > x4 K.E. is constant throughout the region.
B
at x < x1, K.E. is smallest and the particle is moving at the slowest speed.
C
at x = x2, K.E. is greatest and the particle is moving at the fastest speed.
D
at x = x3, K.E. = 4 J.
4
JEE Main 2021 (Online) 27th July Evening Shift
+4
-1
An automobile of mass 'm' accelerates starting from origin and initially at rest, while the engine supplies constant power P. The position is given as a function of time by :
A
$${\left( {{{9P} \over {8m}}} \right)^{{1 \over 2}}}{t^{{3 \over 2}}}$$
B
$${\left( {{{8P} \over {9m}}} \right)^{{1 \over 2}}}{t^{{2 \over 3}}}$$
C
$${\left( {{{9m} \over {8P}}} \right)^{{1 \over 2}}}{t^{{3 \over 2}}}$$
D
$${\left( {{{8P} \over {9m}}} \right)^{{1 \over 2}}}{t^{{3 \over 2}}}$$
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