How Do You Calculate Kinetic Energy and Constant Force in Physics Problems?

[shawli]

Homework Statement

A 5.75 kg object passes through the origin at time t = 0 such that the x component of velocity is 5.00 m/s and its y component of velocity is -3.00m/s.

a) what is the kinetic energy of the object at this time?

b) at t = 2.00s, the particle is located at x = 8.50m and y = 5.00m. What constant force acted on the object during this time interval?

Homework Equations

Change in K = Kfinal - Kinitial
where K = 1/2 * m * v^2

W= force * displacement

The Attempt at a Solution

I got part a by finding the magnitude of the object's velocity then plugging my known values into the K = 0.5mv^2 equation. I got my answer to be K = 97.8J at t=0.

I'm a bit lost on what to do for part b though...

 

[LawrenceC]

You can compute how far the object traveled in 2 seconds. You know its speed at time = 0. Does this information suggest any other equation you might use to compute the average acceleration?

Knowing the average acceleration, you can compute the constant force.

 

[PeterO]

Homework Statement

A 5.75 kg object passes through the origin at time t = 0 such that the x component of velocity is 5.00 m/s and its y component of velocity is -3.00m/s.

a) what is the kinetic energy of the object at this time?

b) at t = 2.00s, the particle is located at x = 8.50m and y = 5.00m. What constant force acted on the object during this time interval?

Homework Equations

Change in K = Kfinal - Kinitial
where K = 1/2 * m * v^2

W= force * displacement

The Attempt at a Solution

I got part a by finding the magnitude of the object's velocity then plugging my known values into the K = 0.5mv^2 equation. I got my answer to be K = 97.8J at t=0.

I'm a bit lost on what to do for part b though...

If the velocity had been unchanged for the 2 seconds, the object will have moved 10.0 in the x direction, and -6 in the y direction.

Instead it ended up where they said.

Treat each dirction separately to find the acceleration in the x-direction and y-direction. COmbine them to find the overall acceleration.

F = ma should give the required force.

 

[shawli]

Thanks!

 

[asteriatic]

I would like to commend your effort in solving the first part of the question. Your approach of using the kinetic energy equation to calculate the object's kinetic energy at t=0 is correct.

For part b, we can use the work-energy theorem to determine the constant force acting on the object during the given time interval. The work-energy theorem states that the work done on an object is equal to the change in its kinetic energy. In this case, we can calculate the change in kinetic energy by subtracting the initial kinetic energy (at t=0) from the final kinetic energy (at t=2.00s).

We can then use the formula W=Fd to calculate the work done on the object, where F is the constant force and d is the displacement of the object during the given time interval. By setting these two equations equal to each other, we can solve for the constant force.

Therefore, the solution for part b would involve calculating the change in kinetic energy and using it in the work-energy theorem to solve for the constant force.