LOM-04-OBJECTIVE UNSOLVED LEVEL - I

OBJECTIVE LEVEL - I 1. A block of mass 10 kg is suspended through two light spring balances as shown in figure. (a) Both the scales will read 10 kg (b) Both the scales will read 5 kg (c) The upper scale will read 10 kg and the lower zero. (d) the readings may be anything but their sum will be 10 kg. 2. A block is kept on the floor of an elevator at rest. The elevator starts descending with an accelera- tion of 12 m/s2. Find the displacement of the block during the first 0.2 s after the start. Take g = 10 m/s2. (a) 10 cm (b) 20 cm (c) 30 cm (d) 40 cm. 3. A body of mass M is kept on a rough horizontal surface (friction coefficient = µ). A person is trying to pull the body by applying a horizontal force but the body is not moving. The force by the surface on body is F where (a) F = Mg (b) F = µ Mg (c) Mg  F  Mg (d) Mg  F  Mg . 4. Which of the following case correctly represents the applied force on a string under tension. End of string is represented with dot. F (a) (b) F (c) (d) . 5. A balloon is descending at a constant acceleration a. The mass of the balloon is M. When a mass m is released from the balloon it starts rising with acceleration a. Assuming that volume does not change when the mass is released, what is the value of m? [Assume same upward buoyant force] 2a M  a  g M (a) (a  g) (b)    2a  (c) 2a (a  g)M (d) Ma a  g . 6. A small cart with a sphere suspended from ceiling by a string is moving up an inclined plane at a speed V. The direction of string supporting the sphere is (a) vertical (b) horizontal (c) perpendicular to the inclined plane (d) none of these. 7. The pulleys and strings shown in the figure are smooth and of negligible mass. For the system of remain in equilibrium, the angle  should be (a) Oº (b) 30º (c) 45º (d) 60º. 8. While walking on ice, one should take small steps to avoid slipping. This is because smaller steps ensure (a) larger friction (b) smaller friction (c) larger normal force (d) smaller normal force. 9. A spring of force constant k is cut into two pieces such that one piece is double the length of the other. Then the long piece will have a force constant of (a) (2/3)k (b) (3/2)k (c) 3k (d) 6k. 10. A simple pendulum is oscillating without damping. When the displacement of the bob is less than maximum, its acceleration vector → is correctly in (a) (b) (c) (d) . 11. A body is moving with a velocity 5 m/s along a straight line. A force of 10 N is applied to the body perpendicular to the line of motion. If the body is of mass 2kg, then the acceleration of the body along the initial straight line of motion is : (a) 5 m/s2 (b) 0 (c) 10 m/s2 (d) none of these. 12. A chain of length L and mass M is hanging by fixing its upper end to a rigid support. The tension in the chain at a distance x from the rigid support is: (a) zero (b) F (L  x) (c) Mg L (d) Mg x . L 13. Two masses m and m are tied with a thread passing over a pulley, m is on a frictionless horizontal surface and m is hanging freely. If acceleration due to gravity is g, the acceleration of m in this arrangment will be (a) g (b) mg/(m + m ) (c) mg/ m (d) mg/(m - m ). 14. A body of mass 60 kg is dragged with just enough force to start moving on a rough surface with coefficients of static and kinetic frictions 0.5 and 0.4 respectively. On continuing (g = 9.8 m/s2) the same force what is the acceleration : (a) 0.98 m/s2 (b) 9.8 m/s2 (c) 0.54 m/s2 (d) 5.292 m/s2 . 15 A block of mass F kg is placed on a rough horizontal surface whose 1 coefficient of fiction is 2 3 . Then the maximum value of force F (shown in figure) such that block doesn’t move (g = 10 m/s2). [JEE 2003] (a) 10 N (b) 20 N (c) 12 N (d) none of these. 16. Which of following respresents 2nd law of motion most correctly. → → (a) → → (b) F  m dv F  ma dt → → (c) F  dp (d) → → . dt F  mv OBJECTIVE LEVEL - II 1. Two objects A and B are thrown upward simultaneously with the same speed. The mass of A is greater than the mass of B. Suppose the air exerts a constant and equal force of resistance on the two bodies. (a) the two bodies will reach the same height (b) A will go higher than B (c) B will go higher than A (d) any of the above three may happen depending on the speed with which the objects are thrown. 2. A block A kept on an inclined surface just begins to slide if the inclination is 300. The block is replaced by another block B and it is found that it just begins to slide if the inclination is 400. (a) mass of A > mass of B (b) mass of A < mass of B (c) mass of A = mass of B (d) all the three are possible. 3. A heavy uniform chain partly lies on a horizontal table. If the coefficient of friction between the chain and the table surface is 0.25, then the maximum fraction of the length of the chain that can hang over edge of the table is (a) 20% (b) 25% (c) 33% (d) 15%. 4. An insect crawls up hemispherical surface very slowly as shown in figure. The coefficient of friction between the insect and the surface is 1/3. If the line joining the centre of the hemispherical surface to the insect makes an angle  with the vertical, the max. possible value of  is given by (a) cot   3 (b) sec   3. (c) cos ec  3. (d) None. 5. A body takes n times, the time to slide down a rough inclined plane as it takes to slide down the same inclined plane when it is perfectly frictionless. The coefficient of kinetic friction between the body and the plane for an angle of inclination of 45º is (a) 1  1 n 1  1  (b) 1 n  1  1 (c)   n 2  (d)  n 2  . 6. A simple pendulum having a bob of mass ‘m’ is suspended from the ceiling of a car used in a stunt film shooting. The car moves up along an inclined cliff at a speed v and makes a jump to leave the cliff and lands at some distance. Let R be the maximum height of car from the top of the cliff. The tension in the string when the car is in air is (a) mg (b) mv 2 mg  mv 2 R (c) mg  (d) zero. R 7. A string of negligible mass going over a clamped pulley of mass m supports a block of mass M as shown in the figure. The force on the pulley by the clamp is given by (a) 2Mg (b) mg (c) (M  m)2  m2 g (d)  (M  m)2  M2 g . 8. The arrangement shown in the figure, the system of masses m , m Rough 1 2 order to prevent the downwards slipping of m2 between m1 and m3 if coefficient of friction between m2 and m3 is µ and all the other sur- faces are smooth, the minimum value of F m2g m2g (a) F  (m1 + m2 + m3) m3 (b) F  (m1 + m2 + m3) m (c) F  (m1 + m2 + m3) g (d) F  (m1 + m2 + m3) g . 9. When a bird of weight W alights on a stretched wire, the tension T in the wire may be: (a) > W/2 (b) = W (c) < W (d) None of these. 10. A block of mass 3kg is at rest on a rough inclined plane as shown in the figure. The magnitude of net force exerted by the surface on the block will be (a) 26N (b) 19.5N (c) 10N (d) 30 N. 3 kg 30º