Two masses $m _ { 1 } = 5 \mathrm {~kg}$ and $m _ { 2 } = 4.8 \mathrm {~kg}$ tied to a string are hanging over a light frictionless pulley. What is the acceleration of the masses when lift free to move ( $\mathrm { g } = 9.8 \mathrm {~m} / \mathrm { s } ^ { 2 }$ )
(1) $0.2 \mathrm {~m} / \mathrm { s } ^ { 2 }$
(2) $9.8 \mathrm {~m} / \mathrm { s } ^ { 2 }$
(3) $5 \mathrm {~m} / \mathrm { s } ^ { 2 }$
(4) $4.8 \mathrm {~m} / \mathrm { s } ^ { 2 }$

A block is kept on a frictionless inclined surface with angle of inclination $\alpha$. The incline is given an acceleration a to keep the block stationary. Then a is equal to
(1) $g/\tan\alpha$
(2) $g\operatorname{cosec}\alpha$
(3) g
(4) $g\tan\alpha$

A body of mass 2 kg slides down with an acceleration of $3 \mathrm {~m} / \mathrm { s } ^ { 2 }$ on a rough inclined plane having a slope of $30 ^ { \circ }$ . The external force required to take the same body up the plane with the same acceleration will be: $\left( \mathrm { g } = 10 \mathrm {~m} / \mathrm { s } ^ { 2 } \right)$
(1) 4 N
(2) 14 N
(3) 6 N
(4) 20 N

A block of mass 10 kg is kept on a rough inclined plane as shown in the figure. A force of $3 N$ is applied on the block. The coefficient of static friction between the plane and the block is 0.6 . What should be the minimum value of force $P$, such that the block does not move downward? (take $g = 10 \mathrm {~ms} ^ { - 2 }$)
(1) 23 N
(2) 25 N
(3) 18 N
(4) 32 N