Instructor: Dr. Tatiana Erukhimova Physics 218: Mechanics Instructor: Dr. Tatiana Erukhimova Lectures 13, 14, 15

Friction everywhere. 2 F 1 Find F necessary to drag the box 1 at constant speed.

The advantage of a pulley What minimum force F is needed to lift the piano of mass M?

A faulty model rocket moves in the xy-plane (the positive y-direction is vertically upward). The rocket’s acceleration has components ax(t)=t2 and ay(t)=-t, where =2.50 m/s4, =9.00 m/s2, and =1.40 m/s3. At t=0 the rocket is at the origin and has velocity with and Calculate the velocity and position vectors as functions of time. What is the maximum height reached by the rocket? What is the horizontal displacement of the rocket when it returns to y=0?

WORK (Chapter 7)

A person carries a bag of groceries of mass M with a constant velocity at the same height from the ground. Find the work done by a person on a bag.

A block of mass m starts at the top of an inclined plane A block of mass m starts at the top of an inclined plane. The coefficient of friction between the plane and the block is . Assuming the block slides down the plane calculate the work done by each force.

First exam Tuesday, September 27, 7 – 8 pm Sections 530, 531 105 HELD Sections 532, 565 107 HELD Section 566 109 HELD

No calculators and cell phones BRING YOUR STUDENT ID! No calculators and cell phones All liquids, gels and aerosols must be in three-ounce or smaller containers.

What is included? Chapters 1-6 Kinematics, vectors, Newton’s laws

Kinematics

In components:

If is given, you can find and

Vectors

Newton’s 2nd Law

Friendly advice DO NOT…

DO NOT use Const acceleration case formulas when acceleration is a function of time. You have to integrate or differentiate! What are the Const acceleration case formulas?

DO NOT write the vector sign over a projection!

DO NOT forget that Fp has two components: Fpcos θ and Fpsin θ Q

Do Not Forget to Write down what is given and express the answer in terms of what is given Box the answer Indicate the origin and positive x and y

Problem 1 p. 122 A man pushes up on a 100 kg block with a force such that it drops from 2 meters to the ground at a constant velocity. How much work is done by gravity? What is the magnitude of the force he exerts?

Work Energy Theorem

M A person is pulling a crate of mass M along the floor with a constant force F over a distance d. The coefficient of friction is . Find the work done by the force F on the crate. Same if F changes as F0(1+x2/d2). Find the work done by the force of friction on the crate (F is constant). Find the net work done on the crate if the crate is pulled with a constant velocity. Find the final velocity of the crate if the crate is pulled with a non-zero acceleration starting from the rest.

Have a great day! Reading: Chapter 7