Question

1. a)When applying Newton's 2nd Law to an object on an inclined plane, we choose the coordinate axes parallel and perpendicular to the plane because

it makes the friction force negligible

it means we do not have to split the gravitational force into two components

it makes acceleration along one axis equal to zero

it makes all the forces sum to zero

all of the above

b) The acceleration of an object of mass m down an incline is equal to g*sin(theta)

always

never

only when the mass is light enough to be assumed negligible

only when there is no friction between the mass and the incline

c and d

c) Consider a mass resting on an inclined plane , The magnitude of the normal force

is equal to the magnitude of the weight

is greater than the magnitude of the weight

is less than the magnitude of the weight

is equal to the gravitational field strength, g

a and d

d) A block sitting on an inclined plane starts to slide down the plane when it is inclined at a given angle. To solve foe the coefficient of static friction between the block and the inclined plane, you need:

only the angle

the mass of the block and the angle

the coefficient of kinetic friction

b and c

this is not in the chapter

e) Consider two masses on a frictionless inclined (ideal) Atwood's machine, In order to solve for BOTH the acceleration of the masses and the tension in the string using Newton's second law, we need to know

both masses, the angle, and the normal force

both masses and the angle but not the normal force

both masses but not the angle and not the normal force

it is not possible to solve for both using Newton's second law; an experiment must be done

it is not possible to solve for both using Newton's second law; conservation of energy must be used

Answer 1

1

a)

The correct choice is :

it makes acceleration along one axis equal to zero

The object moves parallel to the surface of the inclined plane. choosing the coordinate axes parallel and perpendicular to the plane allows us to consider acceleration only along one direction which is easier.

b)

The correct choice is :

only when there is no friction between the mass and the incline.

When there is no friction between the mass and the incline , the mass moves only under the effect of gravity. The component of force of gravity parallel to incline is "mgSin". hence the acceleration experienced by the mass in absence of friction is "gSin".

c)

The correct choice is :

is less than the magnitude of the weight

The normal force on mass resting on inclined plane is balanced by component of force of gravity perpendicular to incline surface.

F_n = mg Cos

Since the value of Cos is less than 1 if the angle is not 0.

F_n is smaller than weight "mg".

d)

The correct choice is :

only the angle

Since the coefficient of static friction on incline surface is given as

= tan

e)

The correct choice is :

both masses and the angle but not the normal force.

For the hanging block force equation can be given as

m₂ g - T = m₂ a                                             Eq-1

For the block on the inclined surface, we have

T - m₁ g Sin = m₁ a                                       Eq-2

Adding Eq-1 and Eq-2

(m₂ g - T) + (T - m₁ g Sin) = m₂ a + m₁ a

a = (m₂ g - m₁ g Sin)/(m₁ + m₂)