Title 2. Low of motion (S.C.Q. ) E.pdf ✅

PHYSICS Q.1 Two small balls of same size and masses m1 and m2 (m1 > m2) are tied by a thin weightless thread and dropped from a certain height. Taking upward buoyancy force F into account the tension T of the thread during the flight after the motion of the balls becomes uniform will be- (A) (m1 – m2)g (B) (m1 – m2) 2 g (C)(m1 + m2)g (D) (m1 + m2) 2 g [B] Sol. Fb = Buoyancy force of air m1 :m1g = T + Fb .......(1) m2 :m2g + T = Fb ....... (2) From eq. (1) & (2) m1g – T = m2 g + T T = 2 (m1 – m2 )g Q.2 A force F is applied to the initially stationary cart. The variation of force with time is shown in the figure. The speed of cart at t = 5 sec is - 10 kg F Parabolic 50 F(N) t(s) 5 (A) 10 m/s (B) 8.33 m/s (C) 2 m/s (D) zero [B] Sol. Parabola has equation t 50 N 5s F F= kt2 ...... (1) 50 = k (5)2 k = 2  F = 2t2 ......... (2)  dt dv m = 2t2   v 0 10 dv = 2 t dt 5 0 2  10 v = 2 5 0 3 3 t         v = 8.33 m/s Q.3 A block of mass 2 kg is sliding with a constant velocity of 8 m/s on a frictionless horizontal surface. The force exerted on the horizontal surface is nearly - (A) 20 N (B) 10 N (C) 40 N (D) 16 N [A] Sol. 2kg 2g v =8m/s force = 2g = 20 N Q.4 Two identical heavy spheres of equal mass are placed on a smooth cup of radius 3r where r is radius of each sphere. Then the ratio of reaction force between cup and any sphere to reaction force between two sphere is – r r 3r 3r O (A) 1 (B) 2 (C) 3 (D) None [B] Sol. 60° R N mg Q. 5 In the figure given below, if all surface are assumed to be smooth and the force F = 100 N. If acceleration of block B of mass 20 kg is 'a' and tension in string connecting block A of mass 20 kg is T,then just after when the force F is applied. A 30o F B (A) T = 0 and a = 5m/s2 (B) T = 100 N and a = 0 (C) T = 200 N and a =5m/s2 (D) None [A] Sol. Conceptual Q. 6 Two identical ideal springs of spring constant 1000 N/m are connected by a pulley as shown in figure and this arrangement is established in the vertical plane. The pulley is ideal and string passing over pulley is massless. At equilibrium of pulley  is 60o and the masses m1 and m2 are 2 kg and 3 kg respectively. Then the elongation in each spring when  is 60o is – m2 m1 Fb Fb m1g T T + m2g