4. An open cart on a level surface is rolling without frictionalloss through a vertical downpour of rain, as shown above. As thecart rolls, an appreciable amount of rainwater accumulates in thecart. The speed of the cart will
(A) increase because of conservation of momentum (B) increasebecause of conservation of mechanical energy
(C) decrease because of conservation of momentum (D) decreasebecause of conservation of mechanical energy
(E) remain the same because the raindrops are falling perpendicularto the direction of the cart's motion
9. A child pushes horizontally on a box of mass m which moves withconstant speed v across a hori¬zontal floor. The coefficient offriction between the box and the floor is µ. At what rate does thechild do work on the box?
(A) µmgv (B) mgv (C) µmg/v (D) µmg/v (E) µmv2
13. Which of the following is true about the net force on anuncharged conducting sphere in a uniform electric field?
(A) It is zero. (B) It is in the direction of the field.
(C) It is in the direction opposite to the field.
(D) It produces a torque on the sphere about the direction of thefield.
(E) It causes the sphere to oscillate about an equilibriumposition.
4. An open cart on a level surface is rolling without frictionalloss through a vertical downpour of rain, as shown above. As thecart rolls, an appreciable amount of rainwater accumulates in thecart. The speed of the cart will
(A) increase because of conservation of momentum (B) increasebecause of conservation of mechanical energy
(C) decrease because of conservation of momentum (D) decreasebecause of conservation of mechanical energy
(E) remain the same because the raindrops are falling perpendicularto the direction of the cart's motion
9. A child pushes horizontally on a box of mass m which moves withconstant speed v across a hori¬zontal floor. The coefficient offriction between the box and the floor is µ. At what rate does thechild do work on the box?
(A) µmgv (B) mgv (C) µmg/v (D) µmg/v (E) µmv2
13. Which of the following is true about the net force on anuncharged conducting sphere in a uniform electric field?
(A) It is zero. (B) It is in the direction of the field.
(C) It is in the direction opposite to the field.
(D) It produces a torque on the sphere about the direction of thefield.
(E) It causes the sphere to oscillate about an equilibriumposition.
