Q5. A bullet of mass 50 g is fired with a speed $100 \mathrm {~m} / \mathrm { s }$ on a plywood and emerges with $40 \mathrm {~m} / \mathrm { s }$. The percentage loss of kinetic energy is :
(1) $84 \%$
(2) $16 \%$
(3) $32 \%$
(4) $44 \%$

Q6. Four particles $A , B , C , D$ of mass $\frac { m } { 2 } , m , 2 m , 4 m$, have same momentum, respectively. The particle with maximum kinetic energy is :
(1) $B$
(2) $A$
(3) $D$
(4) $C$

Q7. To project a body of mass $m$ from earth's surface to infinity, the required kinetic energy is (assume, the radius of earth is $R _ { E } , g =$ acceleration due to gravity on the surface of earth):
(1) $2 m g R _ { E }$
(2) $4 m g R _ { E }$
(3) $m g R _ { E }$
(4) $1 / 2 m g R _ { E }$

Q22. A force $\left( 3 x ^ { 2 } + 2 x - 5 \right) \mathrm { N }$ displaces a body from $x = 2 \mathrm {~m}$ to $x = 4 \mathrm {~m}$. Work done by this force is $\_\_\_\_$ J.