1..An object of massm₁=20kg and velocity

v₁=3.5m/s

crashes into another object of massm₂=9kg and velocity

v₂=15.5m/s.

The two particles stick together as a result of the collision. Because no external forces are acting, the collision does not change the total momentum of the system of two particles, so the principle of conservation of linear momentum applies.

m₁v_1i+m₂v_2i= (m₁+m₂)v_f

If Jed and Kadia use the one-dimensional conservation of momentum equation to find the final velocity of the two joined objects after the collision, what do they obtain? (Indicate the direction with the sign of your answer.) m/s

W :i. w l ., a, O emission 0 sound waves C] energy loss from the change in height of the block PRACTICE IT Use the worked example above to help you solve this problem. The ballistic pendulum (Figure a) is a device used to measure the speed of a fast-moving projectile such as a bullet. The bullet is red into a large block of wood suspended from some light wires. The bullet is stopped by the block, and the entire system swings up to a height h. It is possible to obtain the initial speed of the bullet by measuring h and the two masses. As an example of the technique, assume that the mass of the bullet, m1, is 5.27 g, the mass of the pendulum, m2, is 1.083 kg, and h is 5.14 cm. (a) Find the velocity of the system alter the bullet embeds in the block. m/s (b) Calculate the initial speed of the bullet. EXERCISE HINTS. GETI'INGSTARTED | I'M STUCKI A bullet with mass 5.25 g is red horizontally into a 2.097kg block attached to a horizontal spring. The spring has a constant 5.66 x 102 N/m and reaches a maximum compression of 6.37 cm. (a) Find the initial speed of the bullet-block system. m/s (b) Find the speed of the bullet. m/s 3. [-19.09 Points] . .. G IJIJIH' U 6 Safari File K View His'lo coo = v loll Ewebassignnet Ci / [:35 , Will wlu\";_ w , e * QUESTION When a person is involved in a car accident, why is the likelihood of injury greater in a head-on collision as opposed to being hit from behind? Answer using the concepts of relative velocity, momentum, and average force. (Select all that apply.) C] The average force on the driver is greater in the head-on collision. C] The change in momentum is greater in the head-on collision. Q The collapse of the crumple zone In the front of the car occurs only In the head-on collision. Q The momentum of the driver relative to the ground is greater in a head-on collision. Q The velocity of the driver relative to the ground is greater in a head-on collision. PRACTICE IT Use the worked example above to help you solve this problem. In a crash test, a car of mass 1.40 x 103 kg collides with a wall and rebounds as shown in the gure. The Initial and nal velocities of the car are vi = -15.8 m/s and vf = 2.95 m/s, respectively. If the collision lasts for 0.161 5, nd the following. (a) the impulse delivered to the car due to the collision kg - m/s (b) the size of and direction of the average force exerted on the car (Indicate the direction with the sign of your answer.) EXERCISE HINTS. GETTINGSTARTED | I'M STUCKI Use the values from PRACTICE IT to help you work this exercise. Suppose the car doesn't rebound off the wall, but the time interval of the collision remains at 0.161 s. In this case, the nal velocity of the car is zero. Find the average force exerted on the car. (Indicate the direction with the sign of your answer.) . .. G IJIJIH' U