131. An object at rest explodes into three pieces of equal mass. One of the piece moves eastward at 24 m/s and second moves towards north at 18 m/s. The speed of the third piece is (1) 6 m/s (3) 30 m/s (2) 21 m/s (4) 42 m/s 132. Choose the incorrect statement: (1) Frictional force opposes relative motion between two surfaces in contact. (2) Frictional force is the component of the contact force along the common tangent to the surfaces in contact. (3) Static friction opposes impending relative motion and it always depends on area of contact. (4) Kinetic friction opposes actual relative motion and it is independent of area of contact. 133. A 60 N crate rests on a rough horizontal surface. A 21 N horizontal force is applied on it. If the coefficient of friction are 0.5 and = 0.4, the magnitude of the frictional force on the crate is (1) 9 N (2) 21 N (3) 24 N (4) 30 N 134. A body is moved along a straight line from rest by a machine delivering a constant power. The distance moved by the body is proportional to nth power of time at any instant. Here n is (1) (3) 2 1234 (2) (4) 31211 135. Choose the wrong statement: (1) Every force encountered in mechanics cannot be associated with a potential energy. (2) Work done by friction over a closed path is not zero and no potential energy can be associated with friction. (3) During a collision the kinetic energy conservation (even if collision is elastic) holds at every instant of the collision. (4) During collision the total linear momentum is conserved at each instant of the collision.