1. The problem statement, all variables and given/known data A 5-kg projectile is ﬁred over level ground with a velocity of 200m/s at an angle of 25◦ above the horizontal. Just before it hits the ground its speed is 150m/s. Over the entire trip the change in the internal energy of the projectile and air is: A. +19, 000 J B. −19, 000 J C. +44, 000 J D. −44, 000 J E. 0 I calculated the answer and i got 44000, but i dont know whether its (+) or (-). the answer says its +44000 (C). A 0.75-kg block slides on a rough horizontal table top. Just before it hits a horizontal ideal spring its speed is 3.5m/s. It compresses the spring 5.7 cm before coming to rest. If the spring constant is 1200N/m, the internal energy of the block and the table top must have: A. not changed B. decreased by 1.9J C. decreased by 2.6J D. increased by 1.9J E. increased by 2.6J I got the answer of 2.6J, but again, i dunno whether its (+) or (-). the answer says its -2.6J (B) 33. A block of mass m is initially moving to the right on a horizontal frictionless surface at a speed v. It then compresses a spring of spring constant k. At the instant when the kinetic energy of the block is equal to the potential energy of the spring, the spring is compressed a distance of: A. v√(m/2k) B. (1/2)mv2 C. (1/4)mv2 D. (mv2)/(4k) E. (1/4)√(mv/k) my answer (not listed in choice?): 1/2mv2=1/2kx2 x = v√(m/k) 61. A uniform disk, a thin hoop, and a uniform sphere, all with the same mass and same outer radius, are each free to rotate about a fixed axis through its center. Assume the hoop is connected to the rotation axis by light spokes. With the objects starting from rest, identical forces are simultaneously applied to the rims, as shown. Rank the objects according to their angular accelerations, least to greatest. A. disk, hoop, sphere B. hoop, disk, sphere C. hoop, sphere, disk D. hoop, disk, sphere E. sphere, disk, hoop answer is D, but why is that so? i know the hoop has the greatest rotational inertia, but how is I inversely proportional to angular acceleration? is it because of Torque = I x ∞? A disk starts from rest and rotates around a fixed axis, subject to a constant net torque. The work done by the torque during the second 5 s is ______ as the work done during the first 5 s. A. the same B. twice as much C. half as much D. four times as much E. one-fourth as much I dont understand this question at all, but answer is D.