Physics 218: Mechanics

1
Physics 218 Mechanics
Instructor Dr. Tatiana Erukhimova
Lectures 30, 31, 32
2
Impulse
Changes in a particles momentum are due to
impulse, which depends on the time over which the
net force acts.
3
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.
4
Polar coordinates
5
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?
6
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?
7
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?
8
A 3000 kg spacecraft is in a circular orbit 2000
km above the surface of Mars. How much work must
the spacecraft engines perform to move the
spacecraft to a circular orbit that is 4000 km
above the surface?
9
Rotational Motion
Whirling Beaker of Water
10
Platform rotates with angular acceleration
?(t)?t. A man starts a distance L from the
center and walks in along a straight line painted
on the platform towards the center. He decreases
his distance from the center as a constant rate,
vc. What force does the platform exert on the
man, as a function of his distance from the
center?
11
Conical pendulum
12
A race track designer wants to have the cars able
to maintain a speed vmax without skidding on a
circular track. If the track is flat with a
coefficient of friction ? what does the radius
have to be?
13
A frictionless track contains a circular section
of radius R as shown. What is the minimum height
at which a block must be started in order for it
to go around the loop without falling off the
track?
H
R
14
Kinematics
15
Have a great day! Reading Chapter 12 Hw All
Chapters 12, 13 problems and exercises