Physics 211 exam 1
Figure below shows position of a particle as a function of time for the first 6 seconds of its motion. the average velocity of the particle in the first 3 seconds is
(60-20)/(3-0)= 13.3 m/s
figure 1 shows the position of a particle for the first 10 seconds. The average velocity of this particle during the last four seconds is:
-5 m/s
a ball is thrown with a velocity of 20m/s at an angle of 60 degrees above the horizontal. What is the horizontal component of its instantaneous velocity at the exact top of its trajectory?
10m/s^2 Vx=VocosQ
you can swim in still water at the rate of 3km/h. How long will it take you to move 0.5 km downstream in a river that flows at the rate of 3 km/h?
5 min bc of the total speed of 6km/h
A person with mass 60kg is standing in an elevator that is accelerating upwards with an acceleration a=2 m/s^2. What is the net force on the person
60x2= 120 N
In question 31 above the reaction force of the floor of the elevator is
708 N
The motion of a cart on a straight line is described by v-t graphs as shown below. A(0 to 2s) B(2 to 3s) C(3 to 5s) D(5 to 8s) represent different portions of the motion. In which portion, the total displacement cart is zero
B and D bc they are constant
Three boxes are at rest on a level surface as shown. Forces are applied to the boxes as shown below. which one is going to move in response to the applied force if the coefficient of the static friction between the boxes and the floor is 0.1?
C is was the only positive one
A constant net force acts on a object. Describe the motion of the object.
Constant non-zero acceleration
Figure 2 shows position of a car as a function of time. where is the speed of the car greatest?
D. velocity is greatest where slope is the greatest
The motion of a particle is described in the velocity vs. time graph shown in figure. 3. We can say its speed
Decreases and increases bc it is velocity vs time
T= m(a+g)
EFy= T-mg which equals ma=T=mg which equals T=ma+mg
Suppose that an object is moving with a constant acceleration. Make a statement concerning its motion with respect to time.
In equal times its velocity changes by equal amounts
Who has a greater weight to mass ratio, a person weighing 400 N or a person weighing 600 N?
Neither, their ratios are the same
If you blow up a balloon, and then release it, the balloon will fly away. This is an illustration of
Newton's third law
When is the average velocity of an object equal to the instantaneous velocity?
Only when the velocity is increasing at a constant rate
under what condition is average velocity equal to the average of the object's initial and final velocity?
The acceleration is constant V=Vi=Vo: when velocity is constant
Suppose that a car traveling to the west (-x direction) begins to slow down as it approaches a traffic light. make a statement concerning its acceleration.
The car is decelerating, the acceleration is positive
Suppose that an object travels from one point in space to another. Make a comparison between the displacement and the distance traveled.
The displacement is either less than or equal to the distance traveled
an object is moving to the left at a constant velocity, what can one conclude?
The net force applied to the object is zero
An object of mass m sits on a flat table. The earth pulls on this object with force mg, which we will can action force. What is the reaction force
The object pulling up on the earth with force mg
An object of mass m sits on a flat table. The earth pulls on the object with force mg, which we will call the action force. what is the reaction force?
The object pulling upward on the earth with force mg
It's more difficult to start moving a heavy carton from from the rest than it is to keep pushing it with constant velocity, because
Uk<Uf Static friction is greater than kinetic friction
A net force F accelerates a mass m with an acceleration a. If the same net force is applied to mass 2m, then the acceleration will be
a/2
EFx=F-f
a=[F-us(mg)]/m
the slope of velocity versus time graph gives
acceleration
Action-reaction forces
always act on different objects
The area under a curve in an acceleration versus time graph gives
change in velocity
constant net force equals
constant acceleration
the area under a curve in a velocity versus time graph gives
displacement
Action-reaction forces
equal in magnitude but point in opposite directions
You ride on an elevator that is moving upward with constant speed while standing on a bathroom scale. The reading on the scale is
equal to your true weight, mg
Objects A and B both start from rest. They both accelerate at the same rate. However, object A accelerates for twice the time as object B. What is the distance traveled by object A compared to that of object B?
four times as far
If you are throwing a ball for the second time. If the ball leaves your hand with twice the velocity it had on your first throw, its horizontal range R (compared to your first serve) would be
four times as much.
You are trying to cross a river that flows due south with a strong current. You start out in your motorboat on the east bank desiring to reach the West Bank directly west from your starting point. You should head your motorboat
in the northwesterly direction
A package of supplies is dropped from a plane, and one second later a second package is dropped. Neglecting air resistance, the distance between the falling packages will
increase
Ignoring all air resistance, the horizontal component of a projectile's acceleration
is zero
An object of mass m is hanging by a string from the ceiling of an elevator. The elevator is moving upward, but slowing down. what is the tension in the string
less than mg
force equals
mag
weight:
mass is always the same
in the absence of an external force, a moving object will
move with constant velocity
If the position versus time graph of an object is a vertical line, the object is
moving with infinite speed
If the velocity of an object is zero, does it mean that the acceleration is zero? support your answer with an example
no, an example would be an object starting from rest
For general projectile motion, the horizontal component of a projectile's velocity
remains a non-zero constant
A 20-ton truck collides with a 1500-lb car and causes a lot of damage to the car. Since a lot of damage is done to the car
the force on the truck is equal to the force on the car
If the acceleration vector of an object is directed anti-parallel to the velocity vector,
the object is slowing down
If the acceleration of an object is always directed perpendicular to its velocity,
the object is turning
A bullet is fired horizontally, and at the same instant a second bullet is dropped from the same height. Ignore air resistance. Compare the times of fall of the two bullets.
they hit at the same time
You are standing in a moving bus, facing forward, and you suddenly fall forward. you can imply from this that the bus's
velocity decreased
A rocket moves through empty space in a straight line with constant speed. It is far from the gravitational effect of any star or planet. Under these conditions, the force that must be applied to the rocket in order to sustain motion is
zero
When you sit on a chair, the resultant force on you is
zero
net force equals
zero
