i keep getting 9 m/s for #392, and 225 for #396, am I doing it right and its a mistake, or is EK right?
#392/396 EK 1001 Physics...please help
- Thread starter SAEbrodel
- Start date
- Joined
- Aug 9, 2007
- Messages
- 531
- Reaction score
- 2
No mistakes in the book
392: it's asking what the horizontal velocity will be after the inelastic collision, so you need to use the conservation of momentum to solve it
m1v1 + m2v2 = (m1+m2)v'
the trick here is the 1st ball (m=5kg) is traveling at an angle, so you only take into account the horizontal component of its velocity, or 10cos60 = 5, so if you use 5m/s for it and -10 for the other mass (or switch the signs, whichever way works) and you end up with 7 m/s
5*5 + (-10)*20 = 25*x
-175 = 25x => x=-7 (or in this case to the left)
396:
again it's asking about horizontal momentum, not total momentum, so only take the horizontal component of the momentup into account. the 1st mass is only traveling 5m/s horizontally therefore it's momentum is +25, the 2nd mass is traveling 10 m/s (in the opposite direction) all horizontal therefore its momentum is -200
25 + (-200) = -175, just ignore the sign because they are using to the left as a + and to the right as (-), it works either way
hope this helps
392: it's asking what the horizontal velocity will be after the inelastic collision, so you need to use the conservation of momentum to solve it
m1v1 + m2v2 = (m1+m2)v'
the trick here is the 1st ball (m=5kg) is traveling at an angle, so you only take into account the horizontal component of its velocity, or 10cos60 = 5, so if you use 5m/s for it and -10 for the other mass (or switch the signs, whichever way works) and you end up with 7 m/s
5*5 + (-10)*20 = 25*x
-175 = 25x => x=-7 (or in this case to the left)
396:
again it's asking about horizontal momentum, not total momentum, so only take the horizontal component of the momentup into account. the 1st mass is only traveling 5m/s horizontally therefore it's momentum is +25, the 2nd mass is traveling 10 m/s (in the opposite direction) all horizontal therefore its momentum is -200
25 + (-200) = -175, just ignore the sign because they are using to the left as a + and to the right as (-), it works either way
hope this helps
