# NCERT Physics Class 11 Exemplar Ch 7 System Of Particles And Rotational Motion Part 5

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## One or More then Answer

Q.17. A uniform cube of mass m and side a is placed on a frictionless horizontal surface. A vertical force F is applied to the edge as shown in Fig. Match the following (most appropriate choice):

 (a) (i) Cube will move up. (b) (ii) Cube will not exhibit motion. (c) (iii) Cube will begin to rotate and slip at A. (d) (iv) Normal reaction effectively at from A, no motion.

Answer: (a) ii, (b) iii, (c) i, (d) iv

Q. 18. A uniform sphere of mass m and radius R is placed on a rough horizontal surface (Fig. 7.9). The sphere is struck horizontally at a height h from the floor. Match the following:

 (a) (i) Sphere rolls without slipping with a constant velocity and no loss of energy. (b) (ii) Sphere spins clockwise, loses energy by friction. (c) (iii) Sphere spins anti-clockwise, loses energy by friction. (d) (iv) Sphere has only a translational motion, looses energy by friction.

Answer: (a) iii, (b) iv (c) ii (d) i

Q.19. The vector sum of a system of non-collinear forces acting on a rigid body is given to be non-zero. If the vector sum of all the torques due to the system of forces about a certain point is found to be zero, does this mean that it is necessarily zero about any arbitrary point?