Momentum 2

Q.1. In a crash test a car of mass 1600 kg travelling west at 11 m/s hits a solid concrete wall and comes to rest in a time of 1.5 seconds?

a. What was the momentum of the car before hitting the wall?

b. What was the momentum of the car after hitting the wall?

c. What was the impulse of the collision?

d. What was the force the car exerted on the wall in coming to rest?

e. What was the force the wall exerted on the car in bringing it to rest?

Q.2. In a crash test a crash-test-dummy of mass 120 kg in a car travelling north at 11 m/s hits an air bag and comes to rest in a time of 1.5 seconds?

a. What was the momentum of the dummy before hitting the air bag?

b. What was the momentum of the dummy after hitting the air bag?

c. What was the impulse of the dummy in collision?

d. What was the force the air bag exerted on the dummy in bringing it to rest?

e. What was the force the dummy exerted on the air bag in coming to rest?

Q.3. Abby and Leah were having a game of cricket in the park. Leah bowled a ball (not a cricket ball) of mass 50grams at a speed of 6 m/s and Abby hit it straight back past the bowler at a speed of 14m/s. The bat was in contact with the ball for 0.5 second

a. What was the momentum of the ball when Leah bowled it?

b. What was the momentum of the ball after Abby hit it?

c. What was the change of momentum of the ball from before until after Abby hit it?

d. What was the impulse of the ball in the hit?

e. What was the force the bat exerted on the ball in the hit?

Q.4. Abby was driving a dodgem car south at 4 m/s when it was struck in the rear by Leah's dodgem which was being driven south at 6 m/s The mass of Abby plus her dodgem and backpack was 300kg while the mass of Leah plus her dodgem and backpack was 200 kg. Leah's dodgem continued after the collision with a speed of 4 m/s.

a. What was the total momentum of the two dodgems before the collision?

b. What was the total momentum of the two dodgems after the collision?

c. What was the momentum of Leah's dodgem after the collision?

d. What was the momentum of Abby's dodgem after the collision?

e. What was the speed of Abby's dodgem after the collision? (1 d.p.)

a. What was the momentum of the car before hitting the wall?

p = mv = 1600 x 11 = 17600 Ns (or kgms-2 ) west or towards the wall

b. What was the momentum of the car after hitting the wall?

0 Ns

c. What was the impulse of the collision?

17600 Ns East or away from the wall (Impulse = change of momentum)

d. What was the force the car exerted on the wall in coming to rest?

Ft = 17600 Ns F = 17600/t = 17600/1.5 = 11733N (nearest N) west

e. What was the force the wall exerted on the car in bringing it to rest?

Ft = 17600 Ns F = 17600/t = 17600/1.5 = 11733N (nearest N) east

Q.2. In a crash test a crash-test-dummy of mass 120 kg in a car travelling north at 11 m/s hits an air bag and comes to rest in a time of 1.5 seconds?

a. What was the momentum of the dummy before hitting the air bag?

p = mv = 120 x 11 = 1320 Ns north

b. What was the momentum of the dummy after hitting the air bag?

0 Ns

c. What was the impulse of the dummy in collision?

1320 Ns south (Impulse = change of momentum)

d. What was the force the air bag exerted on the dummy in bringing it to rest?

Impulse = Ft = 1320 F = 1320/1.5 = 880 N south

e. What was the force the dummy exerted on the air bag in coming to rest?

Impulse = Ft = 1320 F = 1320/1.5 = 880 N north

Q.3. Abby and Leah were having a game of cricket in the park. Leah bowled a ball (not a cricket ball) of mass 50grams at a speed of 6 m/s and Abby hit it straight back past the bowler at a speed of 14m/s. The bat was in contact with the ball for 0.5 second

a. What was the momentum of the ball when Leah bowled it?

p = mv = (50/1000) x 6 = 300/1000 Ns = 0.3 Ns towards

b. What was the momentum of the ball after Abby hit it?

p = mv = (50/1000) x 14 = 300/1000 Ns = 0.7 Ns towards Leah

c. What was the change of momentum of the ball from before until after Abby hit it?

Taking towards Leah as positive

Δp = p2 − p1 = 0.7 - - 0.3 = 1.0 Ns towards Leah

d. What was the impulse of the ball in the hit?

Impulse = change of momentum = 1.0 Ns towards Leah

e. What was the force the bat exerted on the ball in the hit?

Impulse = Δp = Ft = 1.0 Ns F = Δp/t = 1/0.5 = 2N towards Leah

Q.4. Abby was driving a dodgem car south at 4 m/s when it was struck in the rear by Leah's dodgem which was being driven south at 6 m/s The mass of Abby plus her dodgem and backpack was 300kg while the mass of Leah plus her dodgem and backpack was 200 kg. Leah's dodgem continued after the collision with a speed of 4 m/s.

a. What was the total momentum of the two dodgems before the collision?

p = 300 x 4 + 200 x 6 = 1200 + 1200 = 2400 Ns south

b. What was the total momentum of the two dodgems after the collision?

2400 Ns south (momentum is conserved)

c. What was the momentum of Leah's dodgem after the collision?

p = mv 200 x 4 = 800Ns south

d. What was the momentum of Abby's dodgem after the collision?

Abby’s momentum = total momentum − Leah’s momentum.

= 2400 − 800 = 1600 Ns south

e. What was the speed of Abby's dodgem after the collision? (1 d.p.)

V = p/m = 1600/300 = 5.3 m/s