- #1
physicos
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Hi everyone , this exercise was given in one of my midterms , but we didn't correct it and I'm wondering where I went wrong on it : Help will be extremely appreciated :
Here is the statement :
A block of mass m=2 kg is pushed by a spring with a spring constant of k=650 N/m which is intially compressed by Δx=0.12m and attached to a wall . This mass slides a distance d= 0.5 m up a frictionless tables which makes an angle θ=6° with the horizontal .
1- What is the expression of the total energy of the mass right when it is pushed by the spring ?
I wrote : E=K+U = 1/2 m*v(t)² + m*g*d(t)*sin θ + 1/2*k*Δx²
The professor wrote on my paper that 1/2 m*v² =0 (WHY ?)
2- What is the expression of kinetic enerfy of the mass when it reaches the edge of the table ?
I wrote ΔK= Wnet =m*g*h+ 1/2*k*Δx² so kowing that Ki=0
Kf= m*g*d*sinθ + 1/2*k*Δx²
The professor said that : Kf= -m*g*d*sinθ + 1/2*k*Δx² (WHY ?)
3- The mass falls a height h=0.8 m down to the ground : With what speed will the block land on the floor :
I used question 2 , having vf= sqrt(2*g*h+k/m*Δx² ) but as 2 was apparently not correct I lost points on it too !
Can anyone help ? THANKS A LOT
Here is the statement :
A block of mass m=2 kg is pushed by a spring with a spring constant of k=650 N/m which is intially compressed by Δx=0.12m and attached to a wall . This mass slides a distance d= 0.5 m up a frictionless tables which makes an angle θ=6° with the horizontal .
1- What is the expression of the total energy of the mass right when it is pushed by the spring ?
I wrote : E=K+U = 1/2 m*v(t)² + m*g*d(t)*sin θ + 1/2*k*Δx²
The professor wrote on my paper that 1/2 m*v² =0 (WHY ?)
2- What is the expression of kinetic enerfy of the mass when it reaches the edge of the table ?
I wrote ΔK= Wnet =m*g*h+ 1/2*k*Δx² so kowing that Ki=0
Kf= m*g*d*sinθ + 1/2*k*Δx²
The professor said that : Kf= -m*g*d*sinθ + 1/2*k*Δx² (WHY ?)
3- The mass falls a height h=0.8 m down to the ground : With what speed will the block land on the floor :
I used question 2 , having vf= sqrt(2*g*h+k/m*Δx² ) but as 2 was apparently not correct I lost points on it too !
Can anyone help ? THANKS A LOT