Calculate acceleration and speed of block

  • #1
chwala
Gold Member
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Homework Statement
A block of wood of mass ##4## kg is released from rest on a plane inclined at ##30^0## to the horizontal. Assuming that the surface is modelled as smooth (no friction), calculate the acceleration of the block, and its speed after it has moved ##3## m.
Relevant Equations
Mechanics
Pretty straight forward, ...reason of posting is to check why i am having a negative value for ##a##.

From my study, i know that

##R(||)## to plane

##F - 40 \cos \dfrac{π}{3} = 4a##

##a = -5 m/s^2##

or can i as well have the equation ( friction and tension are at equilibrium) as,

##40 \cos \dfrac{π}{3} - F = 4a##

For second part,

##v^2 =u^2 +2as##

##v^2= 2×5×3##

...

##v = 5.48 m/s## to two decimal places.
 
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  • #2
chwala said:
Pretty straight forward, ...reason of posting is to check why i am having a negative value for a.
You've chosen down the ramp to be the negative direction!

What is "F" supposed to be in your equation?
 
  • #3
Doc Al said:
You've chosen down the ramp to be the negative direction!

What is "F" supposed to be in your equation?
Friction which is ##0##.
 
  • #4
chwala said:
Assuming that the surface is modelled as smooth (no friction)
If friction is 0, why include it in your equation?
 

FAQ: Calculate acceleration and speed of block

What is the formula to calculate the acceleration of a block?

The formula to calculate the acceleration (a) of a block is derived from Newton's second law of motion, which states that the force (F) acting on an object is equal to the mass (m) of the object multiplied by its acceleration (a). Therefore, the formula is: a = F / m.

How do you determine the speed of a block after a certain time?

The speed (v) of a block after a certain time (t) can be determined using the equation of motion: v = u + at, where u is the initial speed, a is the acceleration, and t is the time elapsed.

What factors affect the acceleration of a block?

The acceleration of a block is affected by the net force acting on it and its mass. According to Newton's second law, a = F / m, where F is the net force and m is the mass. Other factors like friction, air resistance, and incline of the surface can also influence the net force and thus the acceleration.

How can you calculate the net force acting on a block?

The net force (F_net) acting on a block can be calculated by summing all the individual forces acting on it, taking into account their directions. This can include gravitational force, normal force, frictional force, and any applied forces. The net force is given by: F_net = ΣF_i, where ΣF_i represents the sum of all individual forces.

What is the difference between speed and acceleration?

Speed is a scalar quantity that refers to how fast an object is moving, and it is the rate at which distance is covered. Acceleration, on the other hand, is a vector quantity that refers to the rate of change of velocity of an object. Speed has only magnitude, while acceleration has both magnitude and direction.

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