8. A 10-kg ball moving on a horizontal surface recoils from the wall. The force

Question

8. A 10-kg ball moving on a horizontal surface recoils from the wall. The force on the ball during the collision time is shown in the figure for problem 8. The speed of the ball after the recoll is 3 m/s Neglect friction 25) What is the change of the momentum of the ball? d) 100 kg m/s a) 10 kg m/s a) 6 m/s a) did not change b) 30 kg m/s b) 3 m/s b) decreased c) 60 kg m/s c) 5 m/s c) increased 26) What is the initial speed of the ball? d) 9 m/s 27) The kinetic energy of the ball in this collision d) can't be determined

Explanation / Answer

8) 25) The figure should be given, however still answers can be found.

Final momentum = mv = 10*3 = 30 kg m/s

initial momentum is negative = -mu = -10u where u is initial speed

change in momentum = mv - -mu = 30 +10u

option c or d is correct as both are more than 30. If option c is correct then initial speed u is 3 m/s and if d is correct u is 7 m/s. Since in Q26 only 3m/s is given among options, option c is correct not d.

change in momentum = 60 kg m/s option c

26] u = 3 m/s as explain above.

option b is correct.

27] KE did not change as speed is same. option a is correct.

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