Question

a round firecracker at rest on a frictionless ice rink explodes and breaks into 3 pieces that fly apart. the pieces dont fly off the ground, they are all sliding on the flat ice surface. select all of the following statements that must be true after the firecracker exploded. 1) the total kinetic energy of the fragments afterwards is the same as the initial kinetic energy of the fire cracker before the explosion. 2) the total momentum of the fragments is the same as that of the firecracker before the explosion. 3) the total momentum of the fragments is zero.

A. only 1 is true

B. only 2 is true

C. only 3 is true

D. only 1 and 2 is true.

E. all three statements are true

Answer 1

1. Since no dissipating force like friction is acting, so the total energy is conserved. Also all the part stay on the ground and does not fly off so the potential energy is constant so the kinetic energy is also constant that is the total kinetic energy of the fragments after explosion is same as the initial kinetic energy of the firecracker before the explosion.

2. Since no external force act so show the total Momentum is conserved hence total momentum of the fragment is same as that of the firecracker before the explosion.

3. Initially the firecracker was at rest and no external force act on the system so the momentum remains conserved which is equal to zero.

Hence, all the three statements are true.

Hope it helps.