CBSE Class 11 Physics Newton laws of Motion Basic Problems

1. A mass M placed on a smooth table is connected to two light, inextensible strings which pass over opposite edges of the table to hang vertically. Masses m₁, m₂ (m₁ > m₂) are attached to the other ends of the strings. Show that the acceleration of the system when released is m₁- m₂ /m₁+m₂+ M.Find the tensions in the two strings

2. Three blocks A, B and C having masses 2 kg, 1 kg and 3 kg respectivley, are hanging over a fixed pulley as shown. Find the accelerations of the masses and the tensions in the two strings. (g = 10 m/s2)

3. One end of a light string is attached to a 10 kg mass placed on a smooth table. The string passes over the edge of the table and to its other end is attached a light pulley. Over this pulley passes another string having masses 6 kg and 3 kg attached to its ends, Find the 3Kg acceleration of the 10 kg mass. Friction is absent everywhere

4. In the figure, block B weighs 10 N. The coefficient of friction between B and the table is 0.25. Find the maximum weight of block A for which the system will be in equilibrium.

5. In the figure, A is a 10 kg block and B is a 5 kg block.

(a) Find the minimum weight (block C) which must be placed on A to keep it from sliding if μs between A and the table is 0.20
(b) The block C is suddenly lifted off A. What is the acceleration of A if μk between A and the table is 0.15 ?

6. In the given set up, find the acceleration of the blocks and the tensions in the strings. The strings and pulleys P1 and P2 are massless and the inclined plane is fixed. Neglect friction.

7. Two particles of each equal masses m are connected by a light string of length 2l are placedon a smooth horizontal table as shown in figure. A constant force F is applied continuously at the mid-point of the string, always along the perpendicular bisector of the straight line joining the two particles. When the distance between the two particles is 2x, find the acceleration of the particle.

8. Two blocks of masse 2.9 kg and 1.9 kg are suspended from a rigid support S by two inextensible wires each of length one metre, as given in figure. The upper wire has negligible mass and the lower wire has a uniform mass of 0.2 kg/m. The whole system of blocks, wires and support have an upward acceleration of 0.2 m/sec2. Acceleration due to gravity is 9.8 m/sec2. Find the tension

(a) at the middle point of the lower wire.
(b) at the middle point of the upper wire

9. A block of mass 2 kg slides on an inclined plane which makes an angle of 30º with the horizontal. The coefficient of friction between the block and the surfaces is (3/ 2) . (g = 9-8 ms–2)
(a) What force should be applied to the block so that the block moves down without any acceleration?
(b) What force should be applied to the block so that it moves up without any acceleration ?
(c) Calculate the ratio of power needed in the above two cases, if the block moves with the samespeed in both the cases.

10. A bob hanging from the ceiling of a car acts as an accelerometer. Derive a relation for the horizontal acceleration a of the car to the angle θ made by the bob with the verticle. If the brakes are applied, the speed of the car changes from 5 m/s to  5/3 m/s during 3 seconds. Find the angle through which the thread will deflect from the vertical direction. (g = 10 m/sec2).