Transcript Lectures 26, 27, 28

Physics 218: Mechanics
Instructor: Dr. Tatiana Erukhimova
Lectures 26, 27,
28
Average = 73
Median = 77
30
24
26
23
25
18
20
15
9
10
6
5
4
2
2
8
9
0
1
>90
2
3
4
5
6
7
>80 >70 >60 >50 >40 >30 >20 >10
Quiz 2
A block of mass m is sliding on a frictionless
table with velocity v0. It explodes into two
pieces, one with mass m/3. The light piece
flies off horizontally, perpendicular to the
original direction of motion, with velocity 2v0.
Find as many equations as you need to find
the velocity of the heavy piece.
Quiz 3
You are standing on a frictionless surface. Some
idiot throws a rock at you which you catch. In
terms of your mass, the rock’s mass and the
rock’s velocity find your position as a function of
time after you catch the rock.
Problem 4 p.200
In a nuclear collision an incoming proton has
initial velocity of magnitude 3.5 105 m/s. It
collides with another proton, initially at rest.
After the collision one proton goes off at 370 to
the x axis. If the collision is perfectly elastic,
find the velocities of the two protons after the
collision.
Impulse
 t2 


J   Fdt  p2  p1
t1
 dp
F
dt
Changes in a particle’s momentum are due to
impulse, which depends on the time over which
the net force acts.
Impulse
Suppose you throw a ball with a mass of 0.4
kg against a brick wall. It hits the wall moving
horizontally to the left at 30 m/s and rebounds
horizontally to the right at 20 m/s. a) Find the
impulse of the net force on the ball during its
collision with the wall. b) If the ball is in
contact with the wall for 0.010 s, find the
average horizontal force that the wall exerts
on the ball during the impact.
Polar coordinates
A ball of mass m is swung around a circle at the end
of a string of length L. The string will break if the
tension in it exceeds a critical value, Tc. What is the
largest constant angular velocity the ball can have
without breaking the string?
A ball of mass m is swung around a circle at the end
of a string of length L. What is the minimum  the
ball can have and still travel in a circle without string
becoming slack?
A plane is flying in an arc at the speed of v0. At
the top of arc the passengers experience a sense
of weightlessness. What is the radius of the arc?