Why Does Newtonian Physics Say About Object Motion and Forces?

[PhysicsNovice]

Can someone help me with these questions. I am a beginner in the study of physics and would like some help. I have attempted to answer these but would like to know if I am correct and a brief (very brief) explanation. Thanks in advance for your assistance.

An object maintains its state of motion because it has:

a) *mass
b) weight
c) speed
d) acceleration
e) all of these

One object has twice as much mass as another object. The first object also has twice as much:

a) *Inertia
b) Velocity
c) gravitational acceleration
d) volume
e) all of these

A hockey puck is set in motion across a frozen pond. If ice friction and air resistance are neglected, the force required to keep the puck sliding at constant velocity is:

a) *zero Newtons
b) equal to the weight of the puck
c) the weight of the puck divided by the mass of the puck
d) the mass of the puck multiplied by 10 meters per second per second
e) none of these

A 10-N falling object encounters 10 N of air resistance. The magnitude of the net force on the object is:

a) *0 N
b) 4 N
c) 6 N
d) 10 N
e) none of these

The force required to maintain an object at a constant speed in free space is equal to:

a) *Zero
b) the mass of the object
c) the weight of the object
d) the force required to stop it
e) none of these

Neglecting friction, a large block of ice and a small block of ice start sliding down an incline together. The
heavier block will get to the bottom:

a) before the light block
b) after the light block
c) *the same time as the light block

Suppose a particle is accelerated through space by a 10-N force. Suddenly the particle encounters a second force of 10 N in the opposite direction of the first force. The particle is:

a) *brought to a rapid halt
b) decelerates gradually to a halt
c) continues at the speed it had when it encountered the second force
d) theoretically tends to accelerate toward the speed of light
e) none of these

 

[Doc Al]

All correct except this last one.

Suppose a particle is accelerated through space by a 10-N force. Suddenly the particle encounters a second force of 10 N in the opposite direction of the first force. The particle is:

a) *brought to a rapid halt
b) decelerates gradually to a halt
c) continues at the speed it had when it encountered the second force
d) theoretically tends to accelerate toward the speed of light
e) none of these

When that second force acts, what is the net force on the particle?

 

[PhysicsNovice]

Thanks Doc Al. Is the answer (b) decelerates gradually to a halt? The original force of 10N accelerated the object and brought it to a constant velocity. The object would stay at this speed and direction until an unbalanced force acted upon it. At this point the new 10N force applied in the opposite direction would decelerate the moving object a eventually bring it to a halt. I am so confused!? What do you think?

 

[Janus]

Thanks Doc Al. Is the answer (b) decelerates gradually to a halt? The original force of 10N accelerated the object and brought it to a constant velocity. The object would stay at this speed and direction until an unbalanced force acted upon it. At this point the new 10N force applied in the opposite direction would decelerate the moving object a eventually bring it to a halt. I am so confused!? What do you think?

You might want to rethink this, nowhere in the problem does it say that the first force ever stops being applied to the object.

 

[PhysicsNovice]

I am even more confused. Can someone explain? I re-read the question with the clue above in mind. The original 10 N force is constantly applied to the object causing it to accelerate. When the second 10N force is applied to the object in the opposite direction of the original the object will slow slightly but continue to accelerate. Is the answer (d) d) theoretically tends to accelerate toward the speed of light? Thanks for the help.

 

[Doc Al]

The original 10 N force is constantly applied to the object causing it to accelerate.

Right.

When the second 10N force is applied to the object in the opposite direction of the original the object will slow slightly but continue to accelerate.

When that second 10N force is applied: what is the total force on the object?

 

[PhysicsNovice]

0 Newtons? I am not sure.

 

[Doc Al]

0 Newtons? I am not sure.

Eactly right. The force is now zero. So... what's the right answer?

 

[PhysicsNovice]

Doc Al. You have been the only one helping me. Thanks, I feel like I will owe you tutorial service fees. Anyway, after your last reponse I am ready to change my answer to (c) continues at the speed it had when it encountered the second force. His is my new reasoning: A constant 10 N force is applied to the object causing it to accelerate as the force is continually applied. At the moment the second 10 N force is applied in the opposite direction the net acting force is 0 N. At that moment the object would stop its acceleration and the object would continue its speed that it was at the time the second force was applied. If this is correct I do understand this completely. What do you think?

 

[Doc Al]

You got it!

Doc Al. You have been the only one helping me. Thanks, I feel like I will owe you tutorial service fees.

I'm very expensive.

Anyway, after your last reponse I am ready to change my answer to (c) continues at the speed it had when it encountered the second force. His is my new reasoning: A constant 10 N force is applied to the object causing it to accelerate as the force is continually applied. At the moment the second 10 N force is applied in the opposite direction the net acting force is 0 N. At that moment the object would stop its acceleration and the object would continue its speed that it was at the time the second force was applied. If this is correct I do understand this completely. What do you think?

Exactly right.