A force F of strength 20 N acts on an object of mass 3 kg as it moves a distance of 4 In. If F is perpendicular to the 4 [1'1 displacement, the work it does is equal to (A) o J (B) 60 J (C) 80 J (D) 600 J Under the inuence of a force, an object of mass 4 kg accelerates from 3 m/s to 6 m/s in 8 s. How much work was done on the object during this time? (A) 27 J (B) 54 J (C) 72 J (D) 96 J A box of mass m slides down a frictionless inclined plane of length L and vertical height it. What is the change in its gravitational potential energy? (A) mgL (B) mgh (C) -mgL/h (D) -mgh/L While a person lifts a book of mass 2 kg from the oor to a tabletop, 1.5 In above the oor, how much work does the gravitational force do on the book? (A) 30 J (B) 15 J (C) o J (D) 15 J A block of mass 3.5 kg slides down a frictionless inclined plane of length 6.4 m that makes an angle of 30 with the horizontal. If the block is released from rest at the top of the incline, what is its speed at the bottom? (A) 5.0 m/S (B) 6.4 m/s (C) 8.0 m/s (D) 10 m/s Ablock of mass m slides from rest down an inclined plane oflength s and height It. If F is the magnitude of the force of kinetic friction acting on the block as it slides, then the kinetic energy of the block when it reaches the bottom of the incline will be equal to (A) mgh (B) mgs Fh (C) mgh Fs (D) mgs F5 As a rock of mass 4 kg drops from the edge of a 4o-meter-high cliff, it experiences air resistance, whose average strength during the descent is 20 N. At what speed will the rock hit the ground? (A) 10 m/s (B) 12 m/s (C) 16 m/s (D) 20 m/s An astronaut drops a rock from the top of a crater on the Moon. When the rock is halfway down to the bottom of the crater, its speed is what fraction of its final impact speed? (A). 4 (B) 2V2 N/ - A force of 200 N is required to keep an object sliding at a constant speed of 2 m/s across a rough floor. How much power is being expended to maintain this motion? (A) 50 W (B) 100 W C) 200 W D) 400 W