Question

Sammy the mascot runs across the basketball court and dives horizontally. Before he hits the court, the cheer leaders push a large soft pillow in the direction Sammy is running, letting go after a short distance. Sammy lands on the moving pillow, and slides across the floor. Sammy's mass is 60kg, the pillow's mass is 30kg. The pillow is moving at 6m/s and sammy is flying horizontally at 3m/s at the time he lands on the pillow.

1. Draw a FBD of the pillow as it and Sammy slide across the floor.

2. Show the speed of Sammy and the pillow right after Sammy lands on the pillow is 4m/s

3. Determine the amount of energy lost during the collision of Sammy with the pillow.

Answer 1

1)

2) As sammy dives onto the pillow, both moves together, so it is a case of inelastic collision

let s denote sammy and p denote pillow , v_f is the velocity of sammy and pillow together

Using momentum conservation

m_sv_s + m_pv_p = ( m_s + m_p)v_f

60*3 + 30*6 = (60 + 30 ) v_f

180 + 180 = 90 * v_f

v_f = 4 m/s

3) K.E before the collision

K.E = 1/2*60*3*3 + 1/2*30*6*6

K.E = 270 + 540

K.E = 810 JOULES

K.E after collision

K.E = 1/2*90*16

K.E = 720 JOULES

K.E lost = 810 - 720 = 90 joules