Answer Happy

4. The displacement of a particle under several forces is given as: A7=4i-5j +6K (SI) one of the forces is F=-37-57 +9k (SI),the work done by this force over this displacement is ( ) A. -67 J B. 17J C. 67 J D. 91J 5. Several forces applied on a smooth fixed-axis rigid body. If the net force of them is zero. Which statement of the following is correct? ( ) A. The rigid body does not rotate B. The rotating speed of the rigid body does not change C. The rotating speed of the rigid body changes D. The rotating speed of the rigid body may change or may not change. 6. Two particles with masses of m and 4m, and kinetic energies of E and 4E, respectively. They move toward each other along a straight line. The total momentum of them is () A. 2√2mE C. 5√/2mE. D. (2√2-1)√2mE B. 3√/2mE 7. As shown in Fig. 2, A and B are two identical pulleys wrapped with massless ropes. A block of is connected to A and a force acts on B.. The angular accelerations of A and B are and, we have () A. B. mass Sp C. D. first, then Fig. 2 8. A uniformly-charged spherical surface with charge density as .The electric field inside is zero everywhere. The element dS has the charge of ods. The electric field due to the charged element ods inside the spherical surface is ( ) A. zero everywhere. B. not necessarily all zero anywhere C. not zero anywhere. D. unable to determine.