Physics: Forces, Motion, and Energy Key Concepts for Students

Suppose two objects are moving together as a system. If the objects are connected by a string that passes over a pulley, the axis you use to describe the motion should ____________.

follow the curving path of the string

What type of forces affect the motion of a system

eternal forces only

A system consists of two objects, with masses m1 and m2. Using Newton's 2nd Law, complete the formula below for relating the net force Fnet acting on the system to its acceleration a:

Fnet = (m1 + m2) a

An object with mass m is moving with speed v. What is the formula for the kinetic energy K of the object

K = 1/2 mv^2

which of the following statements about energy is true?

Energy can be transferred from on object to another, energy can be transformed from one kind into another,

Ignoring air resistance, which part of the vertical motion has a direct effect on the horizontal motion

none, horizontal motions are independent

fromula for vertical postion yf

yi + viy(t) - 1/2 gt^2

The vertical component of a projectiles motion is

Constant acceleration

What does an IDEAL pulley change?

direction of the string

Which of the following are energy units?

kilowatt-hour & joule

What is the fromula for the final horizontal position xf=

= xi + vixt

The horizontal component of a projectile's velocity is

stays the same

Which of the following equations are correct for converting velocities between frames S and S'?

U = U(prime) + V,

U(prime) = U + V(prime)

Consider two reference frames, S and S', that are moving relative to each other. A particle has velocity u=15 in frame S, and the velocity of S' measured in S is V=6, where positive is to the right. What is u', the velocity of the particle measured in frame S'?

9

Experimenters making measurements in a reference frame ____ be at rest in that frame.

must

The velocity of reference frame S with respect to frame S' is 45 m/s to the north. What is the velocity of frame S' with respect to frame S?

45 m/s south

A particel is moving at speed v around a circular path which has a radius of r. What is the formiula for its angular velocity w?

= v/r

Angular velocity

= w

Suppose you drive around a curve in your car at 20 mph, and then turn around and drive through the same curve at 35 mph. At which speed is your centripetal acceleration largest?

35 mph

Suppose you are driving your car at a constant speed as you round two curves, one whose radius is 1100 m and the second whose radius is 1600 m. For which curve is your centripetal acceleration largest?

1100m, constant speed

A car is traveling west at a constant speed. Without changing speed, if the car starts to turn left then its acceleration is?

South

A particle is moving at speed v along a circular path which has a radius r. What is the formula for its centripetal acceleration ac?

v^2/r

A particle moves a distance s along a circular path with a radius of r. What is the formula for its angular position 𝜃?

𝜃 =

s/r

Which of the following are units of MASS? Choose all that apply.

Kilogram & Gram

Which of the following are units of FORCE?

pound & Newton

If object A has a larger mass than object B, then it will be harder to change the motion of

Object A

Which of the following best describes a force?

A force is an interaction between two objects that can change their motions

An object is acted on by two forces F1 and F2. What is the formula for the net force Fnet acting on the object? (The vector symbols have been omitted for simplicity)

Fnet = F1 + F2

Which of the following forces can be exerted by a surface on an object that is pressed against that surface? Choose all that apply.

friction & normal force

According to Newton's 2nd Law, what is the formula for the acceleration a of and object of mass m that is acted on by a net force Fnet

a = Fnet/m

Which of the following forces act on a box as a person pushes it up a (rough) hill?

weight, normal force, friction & force exerted by the person pushing it

Which of the following forces act on a baseball as it flies through the air (after the person throwing it has let go)?

weight & drag

According to Newton's First Law, there is a direct cause and effect relationship between the unbalanced force applied to an object and its

acceleration

what is the formula for gravitational force?

W = mg

What is the strength of the gravitational field g near the earth?

9.8

What is the gravitation force (near the earth) acting on an object with mass of 10kg

98

Which of the following best describes the direction of the normal force exerted on an object by a surface?

Perpendicular to and away from the surface

Which of the following best describes the direction of the force exerted by a rope on an object?

along the rope, away from where it is attached

What is the formula for the gravitation force?

W= mg

on a free body diagram, one axis should be alogned with?

the direction the object is moving

Which of the following are needed on a free body diagram?

coordinate axes & each force acting on the object

Fnet=?

m x a

What is the formula for the amount of kinetic friction fk

fk = ukn

What is the formula for the maximum amounr of static friction fs if the coefficient of static friction is us and rhe normal force is n?

fs

In problems involving KINETIC friction, what is known?

amount of friction

The coefficient of kinetic friction is ____ the coefficient of static friction

less than

The "job" of friction is to keep (static) or make (kinetic) the acceleration of an object

equal to that of the surface it is pressed against

In problems involving STATIC friction, what is known?

Acceleration of the obejct

When an object reaches terminal speed, the NET FORCE acting on it is exactly equal to ?

0 N

The direction of a drag force is ?

opposite the direction the object is moving

Stokes drag?

force directly proportional to the speed

Newton drag

force directly proportional to the speed squared

Which drag model is most appropriate for slow speeds and or very small objects

Stokes drag

If the speed of an object increases, the magnitude of the drag force acting on it ?

increases

What do forces in action/reaction pair cancel each other out?

only if they act on different parts of the same object

A wandering cow knocks over a fence. The fence falls over due to force exerted BY cow ON fence. the reaction to this for is a force BY ____ ON ______

fence on cow

according to newtons 3rd law, forces in an action/reaction pair are ____ in magnitude and in ______ directions?

Equal and in opposite directions

Whenever two froces are equal and opposite, Newton's 3rd Law is _____ the reason why.

sometimes

According to Newton's 3rd Law, a force is always one member of an action/reaction pair of forces: the force exerted BY object A ON object B and the force exerted BY ____ ON ____

object B ON object A

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