# Hi, I have two homework problems I am having issues with.

1. Two carts of equal mass, m = 0.250 kg, are placed on a frictionless track that has a light spring of force constant k = 53.0 N/m attached to one end of it. The red cart is given an initial velocity of V = 2.55 m/s to the right, and the blue cart is initially at rest.

(a) If the carts collide elastically, find the velocity of the carts just after collision.

(b) If the carts collide, find the maximum compression in the spring.

I know to use conservation of momentum for part a, but I get stuck when I get to this point:

2.55 = v1 + v2 (I cancelled the masses and plugged in the initial velocity for the red cart). How do I determine the value for each velocity?

2.A race car starts from rest on a circular track of radius 370 m. The car's speed increases at the constant rate of 0.730 m/s2. At the point where the magnitudes of the centripetal and tangential accelerations are equal, find the following.

(a)the speed of the race car

(b) the distance traveled

(c) the elapsed time

I set the equations for centripetal and tangential acceleration equal to one another. I converted the linear quantities to angular so all would be equal. To clarify, I used an quation for tangential acceleration (a= rw , where r is radius and w is ang. speed) that is time independent. I found velocity, did a bunch of convertions between tangential and angular, found speed, found the other values, and got the wrong answer. :(

On the first, you also have the conservation of energy: energy is conserved. So use that for a second equation.

2. v^2/r = angular acceleration

.732m/s^2= tangential acceleration

set them equal. solve for v, then for the distance traveled

vfinal=givenabove=acceleration*time

solve for time

distance= vavg*time= vfinal/2 * time

## a. 20 m/s

b. 30 m

## For the first problem, where two carts collide elastically, you are on the right track using conservation of momentum. To determine the value for each velocity, you can set up two equations.

Let v1 be the velocity of the red cart after collision and v2 be the velocity of the blue cart after collision. The equation you have, 2.55 = v1 + v2, represents the conservation of momentum.

To find the second equation, you can use the conservation of energy. Since the collision is elastic, the total mechanical energy before and after the collision is conserved. The initial kinetic energy is given by (1/2)mv^2, where m is the mass (0.250 kg) and v is the initial velocity of the red cart (2.55 m/s). After the collision, the kinetic energy is (1/2)m(v1^2 + v2^2).

Setting these two equations equal, you get (1/2)(0.250)(2.55)^2 = (1/2)(0.250)(v1^2 + v2^2). Now you have two equations with two unknowns.

Solving these equations simultaneously will give you the values for v1 and v2, which are the velocities of the carts after the collision.

For the second problem, where a race car starts from rest on a circular track, you want to find the speed of the race car, distance traveled, and elapsed time when the magnitudes of the centripetal and tangential accelerations are equal.

You correctly set up the equation for tangential acceleration as a = rw, where r is the radius (370 m) and w is the angular speed. The centripetal acceleration is given by a = v^2/r, where v is the speed of the race car.

Setting these two accelerations equal, you get rw = v^2/r. Rearranging this equation, you have v^2 = rw^2. The angular speed, w, can be found using the equation w = w0 + αt, where w0 is the initial angular speed (0) and α is the angular acceleration (0.730 m/s^2).

Substituting this into the equation, you have v^2 = r(0.730)^2t^2. Now you have an equation relating v^2 and t.

To find the speed of the race car (a), you can solve for v using the equation v = √(r(0.730)^2t^2). Substitute the given radius and angular acceleration into the equation, and solve for the speed.

To find the distance traveled (b), you can use the equation d = rθ, where θ is the angular displacement. You can find θ using the equation θ = w0t + (1/2)αt^2. Substitute the given initial angular speed and angular acceleration, and solve for θ. Then substitute into the formula for distance traveled.

To find the elapsed time (c), you can solve for t using the equation v = w0 + αt. Rearrange this equation to solve for t, and substitute the given initial angular speed and angular acceleration.

Remember to consistently use the appropriate units and make sure all calculations are done accurately to get the correct answers.