Calculating Deceleration and Friction of Blocks A & B

[runningirl]

Homework Statement

Block B has an initial velocity of 2.0 m/s to the right and is sliding across the surface of block A. Block A is resting on ideal, frictionless ice. Given the following, information:

a) The rate of "deceleration" of block B
b) The rate of acceleration of block A
c) The final velocity of both blocks. (Block B will come to "rest" on block A when the velocities of both blocks are equal. once the velocities of the two blocks are equal, what will be the frictional force they exert on each other?)

Homework Equations

f=ma

The Attempt at a Solution

for part a:

ma=.3(9.8)(1)

...what do i do for the this problem?
i'm so sorry, but i didn't know where to start at all :(

 

[collinsmark]

Hello Runningirl,

for part a:

ma=.3(9.8)(1)

...what do i do for the this problem?
i'm so sorry, but i didn't know where to start at all :(

Have you left out anything in the problem statement such as the mass of blocks A and B, and the coefficient of kinetic friction between blocks A and B? Or is your answer supposed to be in terms of m_A, m_B and μ?

Whatever the case, for part a) you're supposed to find the magnitude of block B's acceleration. Don't worry about the term "deceleration." It really means the same thing as acceleration, except it has the implication that the acceleration is in the opposite direction as the velocity. So just think of it as the magnitude of block B's acceleration for this problem.

Here is a hint on part b): Newton's third law of motion. Then apply the second law.

 

[runningirl]

Hello Runningirl,

Have you left out anything in the problem statement such as the mass of blocks A and B, and the coefficient of kinetic friction between blocks A and B? Or is your answer supposed to be in terms of m_A, m_B and μ?

Whatever the case, for part a) you're supposed to find the magnitude of block B's acceleration. Don't worry about the term "deceleration." It really means the same thing as acceleration, except it has the implication that the acceleration is in the opposite direction as the velocity. So just think of it as the magnitude of block B's acceleration for this problem.

Here is a hint on part b): Newton's third law of motion. Then apply the second law.

oh, i forgot to add the information:

mass of block a: 3.00 kg and mass of block b: 1.00 kg
the coefficient of kinetic friction between the surfaces of A and B is 0.30
Friction doesn't exist between surfaces of A and the ice.

 

[collinsmark]

Okay, from your original post, you have "ma = 0.3(9.8)(1)". You know what block B's mass is, so solve for a.

See my previous post for hints on part b).

 

[runningirl]

Okay, from your original post, you have "ma = 0.3(9.8)(1)". You know what block B's mass is, so solve for a.

See my previous post for hints on part b).

for part b, do i just do 3*9.8=ma?
but that would say my acceleration is 9.8...

 

[runningirl]

what do you mean by applying Newton's third law?

 

[donutz610]

Always start by drawing a FBD or Free Body Diagram

 

[Paulie323]

as donutz610 said above me drawing a FBD will help clarify in which directions force and accelerations are acting. starting with a proper and correct FBD is the best way to get you started on the right track.

 

[collinsmark]

for part b, do i just do 3*9.8=ma?
but that would say my acceleration is 9.8...

The acceleration isn't 9.8 m/s²

Like others have said, refer to your free body diagram. Drawing one is important.

You don't know what a_A is yet, you're solving for a_A. But if you happen to already know what F_A and m_A are, you should be able to calculate a_A.

what do you mean by applying Newton's third law?

For every action there is an equal and opposite reaction.

You have calculated from part a) that block A exerts a force on block B [Edit: in particular, a horizontal force, in the form of a frictional force]. So what force does block B exert on block A? What is the net force on block A?