At a construction site, a 65.0-kg bucket of concrete hangs from a light (but strong) cable that passes over a light, friction-free pulley and is connected to an 80.0-kg box on a horizontal roof ( Fig. P7.37 ). The cable pulls horizontally on the box, and a 50.0-kg bag of gravel rests on top of the box. The coefficients of friction between the box and roof are shown, (a) Find the friction force on the bag of gravel and on the box. (b) Suddenly a worker picks up the bag of gravel. Use energy conservation to find the speed of the bucket after it has descended 2.00 m from rest. (Use Newton’s laws to check your answer.)
At a construction site, a 65.0-kg bucket of concrete hangs from a light (but strong) cable that passes over a light, friction-free pulley and is connected to an 80.0-kg box on a horizontal roof ( Fig. P7.37 ). The cable pulls horizontally on the box, and a 50.0-kg bag of gravel rests on top of the box. The coefficients of friction between the box and roof are shown, (a) Find the friction force on the bag of gravel and on the box. (b) Suddenly a worker picks up the bag of gravel. Use energy conservation to find the speed of the bucket after it has descended 2.00 m from rest. (Use Newton’s laws to check your answer.)
At a construction site, a 65.0-kg bucket of concrete hangs from a light (but strong) cable that passes over a light, friction-free pulley and is connected to an 80.0-kg box on a horizontal roof (Fig. P7.37). The cable pulls horizontally on the box, and a 50.0-kg bag of gravel rests on top of the box. The coefficients of friction between the box and roof are shown, (a) Find the friction force on the bag of gravel and on the box. (b) Suddenly a worker picks up the bag of gravel. Use energy conservation to find the speed of the bucket after it has descended 2.00 m from rest. (Use Newton’s laws to check your answer.)
A 80.0 kg mail bag hangs by a vertical rope 3.5 m long. A postal worker then displaces the
bag to a position 2.4 m sideways from its original position, always keeping the rope taut.
A 1520-N crate is to be held in place on a ramp that rises at 30.0° above the horizontal (see figure).
The massless rope attached to the crate makes a 22.0° angle above the surface of the ramp. The
coefficients of friction between the crate and the surface of the ramp are uk = 0.450 and us = 0.650.
The pulley has no appreciable mass or friction. What is the MAXIMUM weight w that can be used
to hold this crate stationary on the ramp?
w = ?
Crate
22.0
Ramp
30,0
A desperate hiker has to think fast to help his friend who has fallen below him. Quickly, he ties a rope to a rock of mA = 405 kg
and makes his way over the ledge (see the figure below). If the coefficient of static friction between the rock and the ground is
H=0.348, and the mass of the hiker is ma= 70.1 kg, what is the maximum mass of the friend, mc, that the rock can hold so the
hikers can then make their way up over the ledge? Assume the rope is parallel to the ground and the point where the rope
passes over the ledge is frictionless. (ANS: 70.8 kg)
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