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A bullet with a mass of 19.80 g is fired horizontallyat a block resting on a smo

ID: 1681844 • Letter: A

Question

A bullet with a mass of 19.80 g is fired horizontallyat a block resting on a smooth and frictionless table top. Thebullet embeds itself in the 0.35 kg block. The bullet and blockmove at 2.51 m/s. a. Find the speed of the bullet before it hitthe block. b. What amount ofkinetic energy is lost in the collision for the entire systembullet+block ? a. Find the speed of the bullet before it hitthe block. b. What amount ofkinetic energy is lost in the collision for the entire systembullet+block ?

Explanation / Answer

According to conservation of momentum we have                 m v = (m+ M) V   ==>          v = (m + M) V / m                        = 0.3698 * 2.51 / 0.0198                        = 46.87 m/s Loss in KE = 0.5 (m + M) V2 - 0.5 mv2= 0.5 [ 0.3698 * 2.512 - 0.0198 * 46.872 ] =-20.59 J Here negative sign indicates the loss in kinetic energy.