#### Forces, F=ma, weight, FBD`s

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Transcript Forces, F=ma, weight, FBD`s

An object, subject to several forces, is moving to the right at
constant velocity.
The vector arrows in the figure below represent the forces on the
object. Which of the following force diagrams is correct?
(a)
(b)
(c)
The object below is subject to several forces.
Which of the vector arrows below represent the direction of the
acceleration of the object?
a
1.
2.
3.
b
c
d
e
a0
The thrust force of a rocket remains approximately constant until the
fuel is totally exhausted. While the engine is firing, does the rocket’s
acceleration
(a) increase
(b) decrease
(d) remain the same?
The gravitational force between two objects of mass m1 and m2 ,
separated by a distance r, is given by
m1m2
FG 2
r
The weight of a person of mass m on the Earth’s surface is given by
W = mg
What would the weight of the person be at a height of RE
above the Earth’s surface, where RE is the radius of the
Earth?
(a) mg
(b) 2mg
(d) mg/4
(e) zero
(c) mg/2
The weight of a body of mass m near the Earth’s surface can
be expressed by W=mg.
The gravitational force between two objects of mass m1 and
m2 , separated by a distance r, is given by
m1m2
FG 2
r
If the mass of the Earth is ME and its radius is RE, which of the
following is the correct expression for g?
m1m2
a) g G 2
r
MEm
b) g G
RE 2
ME
c) g G
RE 2
d) None of the above
If the earth had the same mass but twice its radius your weight
at its surface relative to your present weight, be:
a) the same because your mass has not changed
b) twice as large
c) half as larger
d) 4 times as large
e) 1/4 as larger
On the moon, would your weight (as measured on a
bathroom scale) be ?
a) greater then on earth
b) less than on earth
c) the same as on the earth
Why?
A 5.0 kg ball is suspended by light cords
as sketched on the right. Which free body
diagram of point P is most correct?
T1
T1
T2
a)
T2
b)
e) None of the above
T3
T3
T1
T2
c)
T1
T2
d)
T3
T3
For the frictionless pulley system on the right,
is the force F needed to hold the block at a
given height
F
a) greater than mg
b) less than mg
c) equal to mg
Hint: draw a FBD for each
object.
Mass m
Ignoring the mass of the rope in the pulley
system at right, is the force F required to hold
the block at a given height
a) greater than mg
F
b) equal to mg
c) equal to 2mg
d) equal to mg/2
e) greater than 2mg
Hint: draw a FBD for each
object.
m