A cart of mass m is moving with negligible friction along a track with known speed v to the right. It collides 1 with and sticks to a cart of mass 4m moving with known speed v to the right. Which of the two principles, 2 conservation of momentum and conservation of mechanical energy, must be applied to determine the final speed of the carts, and why

Ablock of mass m = 2.5 kg is attached to a spring with spring constant k = 740 n/m. it is initially at rest on an inclined plane that is at an angle of theta= 26 with respect to the horizontal, and the coefficient of kinetic friction between the block and the plane is uk = 0.17. in the initial position, where the spring is compressed by a distance of d = 0.16 m, the mass is at its lowest position and the spring is compressed the maximum amount. take the initial gravitational energy of the block as zero. the block's initial mechanical energy is 9.472 j.b. if the spring pushes the block up the incline, what distance l in meters will the block travel before coming to rest? the spring remains attached to both the block and the fixed wall throughout its motion.