Physics I- Exam #2

When an object is still at rest, f =

f = f_s = -F_ext

What is f_s?

• force of static friction

• when an object is at rest

• has a maximum:

  • f_s,max = μ_sFn where μs is the coefficient of static friction.

When F_ext > f_{s, max}, f becomes the __

force of kinetic friction: f_k = μ_kF_n

In general, is the coefficent of kinetic friction or static friction larger?

μk < μs.

IN general, how do you solve for frictional force?

An object in circular motion must undergo a change in __

velocity → acceleration

Which way does centripetal acceleration point?

toward the center

What is required for centripetal acceleration?

• object at constant speed (but acceleration changing)

• circular path

Work is done when, and only when, an object __

when an object is moved

What are the units for work?

N.m = J

Is work a scalar or vector?

scalar; this means there is only magnitude, no direction and can be +, -, or 0

How do you solve for the scalar (dot) product?

Is kinetic energy a scalar or vector?

scalar

How do you solve for work from a graph?

work = area under the curve

What are the units of power (p) ?

J/s = W (watts)

Work done against a conservative force can be __

recovered (ex: gravitational force)

Non-conservative forces are __

dissipative (ex: friction)

Work done by a conservative force is __ and can be expressed as

is conservative force, can be expressed as potential energy

How do you solve for gravitational potential energy?

What is Hooke’s law?

force exerted on the mass by a spring

• spring force is a conservative force

What is conservation of mechanical energy?

Is momentum a scalar or vector?

vector

What is the law of conservation of linear momentum?

if the sum of the external forces on a system remains zero, the total linear momentum of the system remains constant

During the collision, net force on the system is __

zero. total momentum must be conserved

In elastic collisions, __ is/are conserved.

both momentum (p) and k (kinetic energy)

speed of separation = speed of approach

In elastic collisions, __ is conserved

p is conserved, k is not

Wa=hat is the coefficient of restitution?

measure of elasticity of a collision closer to 0 = more perfectly inelastic

between 0 and 1

In perfectly inelastic collisions, __

objects stick together

What is the e value for elastic and perfectly inelastic collisions?

• elastic: e=1

• perfectly inelastic: e=0

What is center of mass?

“mean location” of all the mass in the system/object