Laws of Motion Questions and Answers Part-19

1.Three blocks of masses \[m_{1},m_{2}\]  and \[m_{3}\] are connected by massless strings as shown on a frictionless table. They are pulled with a force \[T_{3}=40N\]  . If \[m_{1}=10kg\]   , \[m_{2}=6kg\]  and \[m_{3}=4kg\]  , the tension \[T_{2}\] will be
a) 20 N
b) 40 N
c) 10 N
d) 32 N

Answer: d

2. A block of mass \[m_{1}\] rests on a horizontal table. A string tied to the block is passed on a frictionless pulley fixed at the end of the table and to the other end of string is hung another block of mass \[m_{2}\] . The acceleration of the system is
a) \[\frac{m_{2}g}{\left(m_{1}+m_{2}\right)}\]
b) \[\frac{m_{1}g}{\left(m_{1}+m_{2}\right)}\]
c) g
d) \[\frac{m_{2}g}{m_{1}}\]

Answer: a
Explanation: \[\frac{m_{2}g}{\left(m_{1}+m_{2}\right)}\]

3. A 2 kg block is lying on a smooth table which is connected by a body of mass 1 kg by a string which passes through a pulley. The 1 kg mass is hanging vertically. The acceleration of block and tension in the string will be
a) \[3.27m\diagup s^{2},6.54 N\]
b) \[4.38m\diagup s^{2},6.54 N\]
c) \[3.27m\diagup s^{2},9.86 N\]
d) \[4.38m\diagup s^{2},9.86 N\]

Answer: a

4. A light string passes over a frictionless pulley. To one of its ends a mass of 6 kg is attached. To its other end a mass of 10 kg is attached. The tension in the thread will be
a) 24.5 N
b) 2.45 N
c) 79 N
d) 73.5 N

Answer: d

5. Two masses of 5kg and 10kg are connected to a pulley as shown. What will be the acceleration of the system (g= acceleration due to gravity)
a) g
b) \[\frac{g}{2}\]
c) \[\frac{g}{3}\]
d) \[\frac{g}{4}\]

Answer: c

6. A block A of mass 7 kg is placed on a frictionless table. A thread tied to it passes over a frictionless pulley and carries a body B of mass 3 kg at the other end. The acceleration of the system is \[\left(g=10m s^{-2}\right)\]
a) \[100m s^{-2}\]
b) \[3m s^{-2}\]
c) \[10m s^{-2}\]
d) \[30m s^{-2}\]

Answer: b

7. Three blocks of masses 2 kg, 3 kg and 5 kg are connected to each other with light string and are then placed on a frictionless surface as shown in the figure. The system is pulled by a force \[F=10N\]  , then tension \[T_{1}=\]
a) 1N
b) 5 N
c) 8 N
d) 10 N

Answer: c

8. A light string passing over a smooth light pulley connects two blocks of masses m1 and m2 (vertically). If the acceleration of the system is g/8 then the ratio of the masses is
a) 8 : 1
b) 9 : 7
c) 4 : 3
d) 5 : 3

Answer: b

9. Two masses \[m_{1}=5 kg\]  and \[m_{2}=4.8kg\]   tied to a string are hanging over a light frictionless pulley. What is the acceleration of the masses when they are free to move \[\left(g=9.8m\diagup s^{2}\right)\]
a) \[0.2m\diagup s^{2}\]
b) \[9.8 m\diagup s^{2}\]
c) \[5m\diagup s^{2}\]
d) \[4.8m\diagup s^{2}\]

Answer: a

10. A block of mass 4 kg is suspended through two light spring balances A and B. Then A and B will read respectively
a) 4 kg and zero kg
b) Zero kg and 4 kg
c) 4 kg and 4 kg
d) 2 kg and 2 kg

Answer: c
Explanation: As the spring balances are massless therefore the reading of both balance should be equal.