just problem 6 & 7 ases a hathroom scale to measure the upward force exerted on
ID: 2032000 • Letter: J
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just problem 6 & 7
ases a hathroom scale to measure the upward force exerted on his feet. As the elevator lows to a stop, the scale reads 790N. (a) What force magnitude does the scale read when the elevator is traveling at constant velocity? (b) What is the magnitude and direction of the Probtem 5r A 6o kg perso is riding ia clevawr tdhat is ascending to the wp loor of the acceleration as the clevator is coming to a stop? Eiffel Tower with a speed of 18 m/s. As it approaches the top level, the clevator takes 4.2 seconds to stop. (a) What is the person's apparent weight before the elevator begins to slow down? (b) What is the elevator's acceleration while stopping at the top floor? (c) What is the person's apparent weight while the elevator is coming to a stop? Problem 6: In the figure, two wooden blocks are connected by a string that passes over a very light frictionless pulley. One block slides on a horizontal table (M 5-kg), while the other hangs suspended by the string (m - 3-kg). At time t-0, the suspended block is 1.8 m over the floor, and the blocks are released from rest. After 2.5 s, the suspended block reaches the floor. Massless string Massless, fric tionless pulley What is the acceleration of the 3-kg block? What is the tension in the string attached to the 5-kg block? What is the coefficient of kinetic friction between the table and the sliding block? Problem 7: A worker in a warchouse pushes a 25-kg crate across a horizontal floor. The coefficient of kinetic friction between the crate and the floor is 0.28. The box moves across the floor at a constant 7 m/s. How hard is the worker pushing on the box? The werker lets go of the crate and lets it slide. What is the net acceleration of the box after the worker lets go? How far does the crate travel from the time the worker lets it go until it comes to rest? Short Answer 1: True or False: In order to get an object moving, you must push harder on it than it pushes back on you. Explain. Short Answer 2: A wooden block B has twice the mass of wooden block A. A hand is applying a force to block A, which is moving to the right with constant speed. Rank in order, from largest to smallest, the magnitudes of all the horizontal forces acting on the system. Friction is not negligible.Explanation / Answer
6) from the given information, we will have two equations
T - FK = Ma ------------------ (1) (from block on the table)
mg - T = ma -------------------- (2) ( from hanging block)
solving (1) and (2) , we get
mg - ukMg = ( m + M )a
a = mg - ukMa / m + M ----------------- (3)
to find a, we use kinematics,
H = ut + 1/2at2
1.8 = 1/2*a*(2.5)2
a = 0.576 m/s2
Put in (3) to get uk and then use either of equation (1) or (2) to get T
0.576 = 3*9.8 - uk*5*9.8 / 5+3
0.576 = 29.4 - 49*uk / 8
4.608 = 29.4 - 49*uk
24.792 = 49*uk
uk = 0.5059
T = 5*0.576 + 0.5059*5*9.8
T = 27.67 N
7) He needs to overcome friction. It is given as
fk = uk mg = - 0.28*25*9.8 = 68.6 N. So worker must be pushing at 68.6 N
a = fk / m = - 68.6 / 25 = - 2.744 m /s2
use kinemtics to find distance travlled.
vfinal2 - vinitial2 = 2ax
vfinal = 0 (block comes to rest)
-49 = - 5.488x
x = 8.928 m
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