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Problems

This document contains descriptions of 15 physics problems involving forces, masses, and motion. Problem 2.11 asks to find the acceleration of a block sliding on a wedge being pushed with constant acceleration. Problem 2.12 asks to find the acceleration of a painter pulling himself up by two ropes over pulleys. Problem 2.15 asks to find the immediate acceleration of mass mA after a catch is removed, allowing the masses mA and mB connected by a string on a rotating disk to slide.

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447 views1 page

Problems

This document contains descriptions of 15 physics problems involving forces, masses, and motion. Problem 2.11 asks to find the acceleration of a block sliding on a wedge being pushed with constant acceleration. Problem 2.12 asks to find the acceleration of a painter pulling himself up by two ropes over pulleys. Problem 2.15 asks to find the immediate acceleration of mass mA after a catch is removed, allowing the masses mA and mB connected by a string on a rotating disk to slide.

Uploaded by

viking6461
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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PROBLEMS 79

(a) Draw force diagrams, and show all relevant coordinates.


(b) How are the accelerations related?
y 2.11 Mass on wedge*
m A 45◦ wedge is pushed along a table with constant acceleration A.
x A block of mass m slides without friction on the wedge. Find the
A block’s acceleration. Gravity is directed down.

2.12 Painter on scaffold*


A painter of mass M stands on a scaffold of mass m and pulls
himself up by two ropes which hang over pulleys, as shown.
He pulls each rope with force F and accelerates upward with
a uniform acceleration a. Find a—neglecting the fact that no one
could do this for long.

2.13 Pedagogical machine*


A “pedagogical machine” is illustrated in the sketch. All surfaces
are frictionless. What force F must be applied to M1 to keep M3
from rising or falling?

M2

F
M1 M3

2.14 Pedagogical machine 2*


Consider the “pedagogical machine” of the previous problem in
the case where F is zero. Find the acceleration of M1 .

2.15 Disk with catch


mB w A disk rotates with constant angular velocity ω, as shown. Two
masses, mA and mB , slide without friction in a groove passing
through the center of the disk. They are connected by a light string
ra of length l, and are initially held in position by a catch, with mass
l
mA at distance rA from the center. Neglect gravity. At t = 0 the
catch is removed and the masses are free to slide.
mA Find r̈a immediately after the catch is removed, in terms of mA ,
mB , l, rA , and ω.

2.16 Planck units*


Max Planck introduced a constant h, now called Planck’s constant,
to relate the energy of an oscillator to its frequency. h = 6.6 ×
10−34 J · s, where 1 joule (J) = 1 newton-meter. (h is engraved on
Planck’s tombstone in Göttingen, Germany.)

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