Three forces act on an object. If the object is in translational equilibrium, wh
ID: 1646224 • Letter: T
Question
Three forces act on an object. If the object is in translational equilibrium, which of the following must be true? I. The vector sum of the three forces must equal zero. II. The magnitudes of the three forces must be equal. III. All three forces must be parallel. (A) I only (B) II only (C) I and III only (D) II and III only (E) I, II, and III A child pushes horizontally on n box of mass m which moves with constant speed v across a horizontal floor. The coefficient of friction between the box and the floor is mu. At what rate docs the child do work on the box? (A) mu mgv (B) mgv (C) v/mu mg (D) mu mg/v (E) mu mv^2 A block of mass 3.0 kg is hung from a spring, causing it to stretch 12 cm at equilibrium, as shown above. The 3.0 kg block is then replaced by a 4.0 kg block, and the new block is released from the position shown above, at which the spring is unstretched. How far will the 4.0 kg block fall before its direction is reversed? (A) TOC o "1-5" h zExplanation / Answer
6.For the body to be in translational equilibrium,the vector sum of the three forces acting on it must be equal to zero.Hence,answer is option A.
7.Since velocity is constant,acceleration =0.Therefore we need to consider only the force required to overcome friction.Frictional force Ff =coefficient of friction X Weight=uXmg=umg
Work done=FfXdistance s=umgs
Rate of work=Work/Time=umgs/t=umgv since v=s/t. Option A
8.F=kx can be equated to weight W=mg
ie, kX0.12=3X9.8, k=3X9.8/0.12=245
At the point of release only potential energy is present.PE=mgh
At the point of turning,only spring energy exists.U=0.5kh2
Equating the two,mgh=0.5kh2 or h=2mg/k=2X4X9.8/245=0.32m=32cm Option D
9.Gravitational force Fg=GMM/r2 .ie,Fg is inversely proportional to r2. Fg2/Fg1=W2/W1=r12 /r22 =r2/16r2 =1/16
ie,W2 =W1/16 Option E