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Jim Guinn’s PHYS2211 Assignment #11 Solutions
These problems are not to be turned in.
They are for you to study for the exam.
1. A car has a mass of 1500kg.
A truck has a mass of 19000kg and is moving at 30m/s .
a.)
At what speed would the car have the same magnitude of momentum as the truck?
To have equal momenta we have
m
c
v
c
= m
t
v
t
or
v
c
= m
t
v
t
/ m
c
= (19000kg) (30m/s) / (1500kg) =
v
c
= 380m/s !
b.)
At what speed would the car have the same kinetic energy as the truck.
To have equal kinetic energies we have
(1/2)m
c
v
c
2
= (1/2)m
t
v
t
2
or
v
c
2
= m
t
v
t
2
/ m
c
= (19000kg) (30m/s)
2
/ (1500kg) = 11400m
2
/s
2
, so
v
c
= 107m/s .
Quite a bit less!
2. A 5.00kg mass is dropped (from rest) from 2.00m above the top of a large, vertically
aligned spring.
The spring has a spring constant of 100N/m .
You must solve this using
Conservation of Energy.
(Hint: where do you want the gravitational potential energy equal to
zero?)
We set the gravitational and elastic potential energies at zero at the equilibrium point for
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 Spring '11
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