a) He simultaneously throws both stones horizontally off the back of the wagon.

Question

a) He simultaneously throws both stones horizontally off the back of the wagon. The stones fly out of his hand with a speed of 8 m/s relative to Taqwaan. How fast is the wagon moving forward afterwards?

b) He stops and gets out of the wagon, gathers up the stones, and sits in the motionless wagon again. This time, he throws the stones out one at a time; each stone again leaves his hand at a speed of 8 m/s (relative to him).

i. How fast is he moving after he has thrown the first stone?

ii. How fast is he moving after he has thrown the second stone?

The answers should be:

a) 1.45 m/s

b) i. 0.73 m/s

ii. 1.53 m/s

Please explain how to get to these answers.

Explanation / Answer

from the given

m1 = 35 kg + 10 kg

= 45 kg

u1 = u2

= 0

m2 = 10 kg

v1 = ?

v2 = 8 kg

according to the law of conservation of linear momentum

m1 u1 + m2 u2 = m1 v1 + m2 v2

since the boy is sitting before the throw

u1 - u2 = 0

0 = m1 v1 + m2 v2

m1 v1 = - m1 v2

solve for v1

v1 = -(10 x 8 / 45)

= ......... m / s

the negative sign indicated that both are moving in opposite direction

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