# Find the distance that the block has to move so that....

• Like Tony Stark
In summary: What has that got to do with whether the block and the cylinder have the same acceleration? The cylinder starts from rest, so it accelerates.
Like Tony Stark
Homework Statement
The picture shows a block of ##m=2 kg## which moves along a cylinder with constant velocity ##1 \frac{m}{s}## relative to Earth due to the force applied in the photo. The coefficient of dynamic friction between the cylinder and the block is ##0.3## and ##0## between the cylinder and the Earth. Determine the distance with respect to the Earth that the block should move so that it moves ##0.05 m## with respect to the cylinder which was static at first.
Relevant Equations
Newton's equations
I called the block ##A## and ##B## the cylinder. For ##A##, in the non inertial system I wrote
##x) Fr_d -F=0##
##y) R-W_1=0##
Where ##Fr_d## is the kinetic friction and ##R## the normal force on ##A##

Then, I know that:
##a_{B/A}=a_B-a_A##
##0=a_B -a_A##
##a_A=a_B##

##v_{B/A}=v_B-v_A##
##v_{B/A}=v_B-(-1;0)##

But if the velocity of ##A## is constant, then it has no acceleration and so ##a_B=0## and then ##x_A=-t## so I just have to replace with ##-0.05##

#### Attachments

• 20191006_011341.jpg
25.3 KB · Views: 176
The question seems incomplete.
No mass is specified for the cylinder. If massless it will move with the block.
Even if it has a known mass, the only horizontal force is the friction from the block, so it will accelerate until it matches the block's speed, so we need to be told e.g. that the cylinder starts at rest.

I
haruspex said:
The question seems incomplete.
No mass is specified for the cylinder. If massless it will move with the block.
Even if it has a known mass, the only horizontal force is the friction from the block, so it will accelerate until it matches the block's speed, so we need to be told e.g. that the cylinder starts at rest.
It does say that the cylinder starts at rest. The last sentence states "the cylinder which was static at first"

Like Tony Stark said:
I

It does say that the cylinder starts at rest. The last sentence states "the cylinder which was static at first"
Ah, yes... but you still need the mass of the cylinder.

M
haruspex said:
Ah, yes... but you still need the mass of the cylinder.
My bad, I didn't write it. It says its mass is ##4 kg##

Like Tony Stark said:
My bad, I didn't write it. It says its mass is ##4 kg##
Ok.
So in post #1, why have you written that the two objects have the same acceleration?

haruspex said:
Ok.
So in post #1, why have you written that the two objects have the same acceleration?
Bevause it says that the block has constant velocity so it has no acceleration

Like Tony Stark said:
Bevause it says that the block has constant velocity so it has no acceleration
What has that got to do with whether the block and the cylinder have the same acceleration? The cylinder starts from rest, so it accelerates.

## 1. How do you calculate the distance that a block needs to move?

The distance that a block needs to move can be calculated using the formula: distance = velocity x time. This formula takes into account the speed at which the block is moving and the amount of time it takes to cover that distance.

## 2. What is the difference between distance and displacement?

Distance refers to the total length of the path covered by an object, while displacement refers to the straight-line distance between the starting and ending points of an object's motion. Displacement takes into account the direction of motion, while distance does not.

## 3. Can the distance that a block has to move be negative?

No, distance is a positive quantity and cannot be negative. However, displacement can be negative if the object moves in the opposite direction of its initial position.

## 4. Does the mass of the block affect the distance it has to move?

No, the mass of the block does not affect the distance it has to move. The distance is solely dependent on the velocity and time.

## 5. What units are used to measure distance?

Distance can be measured in various units, such as meters, kilometers, feet, miles, etc. The choice of unit depends on the scale of the object or distance being measured.

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