Please write your homework neatly. Don't try to cram all the problems into the
minimum space. Show your work clearly, and useful diagrams are always appropriate
and may get extra points. You may work with others, but the work should be your
own. I expect numeric answers to have a reasonable number of significant figures
and proper units.
Note: WebAssign grades only on the answer; I will grade only (mostly) on the
method! Make your method clear.
1. Cummings et al., Ch. 6, p. 175, Problem 87
2. Cummings et al., Ch. 6, p. 177, Problem 100
| 3. You are moving a box along a horizontal surface, either by pushing it, or pulling it. In both cases your pull or push makes an angle theta with the horizontal. You can assume that you know the push, P, the angle, theta , and the mass of the box, m, as well as the value g. Only these symbols and later µ (mu) can appear in your answers. | |
(0) Always begin by drawing a force diagram for the block.
(a) First consider the case of no friction acting between the box and the table.
(i) What is the acceleration of the box in each
case?
(ii) What is the normal force in each case?
(b) Now suppose that there is friction, with a coefficient of friction µ
(mu) between the box and the table. Also assume that the box is in motion to
the right. What is the acceleration of the box in each case?
(c) Finally, suppose that the box is moving to the left, and you are trying
to stop it. What is the acceleration of the box in each case?
| 4. Consider two blocks sitting on top of each other on a horizontal surface. The top block has mass m1 = 5.0 kg and the bottom block has a mass of m2 = 25.0 kg. Between the blocks there is friction with coefficients of friction of µs(mu-static) = 0.45 and µk (mu kinetic)= 0.40. The table is very smooth and there is no friction between the bottom block and the table. You attach a string to the top block and pull with a pull P at an angle theta = 37° to the horizontal. |  |
You should solve each part of the problem using symbols and
then plug in numbers.
(a) You apply a large pull P = 25 N and the blocks slide relative to each other.
Draw a free body diagram for each block separately.
(b) Solve for the normal force between the blocks, and then find the friction
force between the blocks.
(c) Find the accelerations of the blocks (two different values).
(d) Now you apply a small force of P = 12.0 N and the blocks move together.
Find the common acceleration of the blocks.
(e) Now find the force of static friction between the blocks – the actual
force, not the maximum value.
BONUS (f) If you want the two blocks to move together with the same velocities,
what is the maximum pull you can apply?
This page maintained by Anne G. Young. Last modified 07-Oct-2004 .