Change in kinetic energy Velocity not given

AI Thread Summary
The discussion revolves around calculating the change in kinetic energy of a block subjected to two opposing forces on a frictionless surface. The initial and final positions of the block are provided, but the final velocity is not given, leading to confusion about how to proceed. Participants suggest using the work-energy principle, stating that the change in kinetic energy equals the work done on the block, which can be determined using the net force and displacement. Ultimately, the original poster expresses gratitude for the clarification and confirms understanding of the solution. The key takeaway is that the change in kinetic energy can be calculated using the forces and displacement, despite the absence of velocity.
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change in kinetic energy! Velocity not given :(

Homework Statement


Two forces, of magnitudes F1 = 70.0 N and F2 = 35.0N , act in opposite directions on a block, which sits atop a frictionless surface, as shown in the figure. Initially, the center of the block is at position xi = -2.00cm . At some later time, the block has moved to the right, and its center is at a new position, Xf = 4.00 cm .

Determine the change in the kinetic energy of the block as it moves from Xi= -2.00 to X f= 4.00

Link to the diagram : http://session.masteringphysics.com/problemAsset/1011314/13/MWE_wi_5.jpg

Homework Equations


Kinetic energy = 1/2 mv^2


The Attempt at a Solution



Since it is starting from rest, initial velocity, V0 = 0 and then d = Vf t

But here Vf is not given..
I am not sure how to proceed when there is no velocity given

Can any more help me ?

Thanks a lot before hand
 
Last edited:
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rock_star said:

Homework Statement


Two forces, of magnitudes F1 = 70.0 N and F2 = 35.0N , act in opposite directions on a block, which sits atop a frictionless surface, as shown in the figure. Initially, the center of the block is at position xi = -2.00cm . At some later time, the block has moved to the right, and its center is at a new position, Xf = 4.00 cm .

Determine the change in the kinetic energy of the block as it moves from Xi= -2.00 to X f= 4.00

Link to the diagram : http://session.masteringphysics.com/problemAsset/1011314/13/MWE_wi_5.jpg

Homework Equations


Kinetic energy = 1/2 mv^2


The Attempt at a Solution



Since it is starting from rest, initial velocity, V0 = 0 and then d = Vf t

But here Vf is not given..
I am not sure how to proceed when there is no velocity given

Can any more help me ?

Thanks a lot before hand

What is the net force acting on the block? Just keep the mass and velocity as variables, m and V for now. Write the equations to tell you how long it takes to get to the 2nd position, and what the final velocity is. Then see if some of the variable terms cancel out...
 


Change in kinetic energy = work done on the block = Force X displacement.
In the problem force and displacement is given. That is sufficient to find the KE.
 


Thank a lot everyone! :)
I understood it! :D
Thank a ton everyone!
 
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