Transcript practice problems

A
fan and a sail are mounted vertically on a cart
that is initially at rest on a horizontal table as shown:
When the fan is turned on
fan
air
an air stream is blown towards
the right and is incident on the
sail. The cart is free to move with
negligible resistance forces.
After the fan has been turned on the cart will
A.
move to the left and then to the right.
B.
remain at rest.
C.
move towards the right.
D.
move towards the left.
sail
Types of Collisions
Elastic Collisions
Objects bounce off each
other with no loss of
energy (no damage or
deformation is done to
either object)
Inelastic Collisions
Objects collide, but
damage/deformation/sticking
will occur to some extent
Some of the original energy is
used in compression or
breaking, or is converted to
sound, heat, etc.
Total momentum remains constant
Total kinetic energy
remains constant
Kinetic energy is NOT
conserved
Examples:
atoms, magnetic bumpers
bug hitting a windshield; baseball
bat against baseball
#1
•A rubber ball with a mass of 0.185 kg is
dropped from rest. From what height was
the ball dropped, if the magnitude of the
ball's momentum is 0.720 kg · m/s just
before it lands on the ground?
#2
• A member of the volleyball team spikes the ball.
During this process, she changes the velocity of
the ball from 5.2 m/s to −23.3 m/s along a
certain direction. If the impulse she delivers to
the ball is −7.8 kg · m/s, determine the mass of
the volleyball.
#3
• A particle with a mass of 1.25 kg is acted on by a force Fx acting in
the x-direction. If the magnitude of the force varies in time as shown
in the figure below, determine the following.
• Impulse of the force
• Final velocity of the particle
(assume u=0 m/s)
• Final velocity of the particle if
u = -1.50 m/s
#4
A professional boxer hits his opponent with a 1175-N
horizontal blow that lasts 0.160 s. The opponent's total
body mass is 119 kg and the blow strikes him near his
center of mass and while he is motionless in midair.
Determine the following.
(a) impulse the boxer imparts to his opponent by this
blow
(b) the opponent's final velocity after the blow
#5
• Two ice skaters stand facing each other at rest on a
frozen pond. They push off against one another and
the 48-kg skater acquires a speed of 0.62 m/s. If the
other skater acquires a speed of 0.83 m/s, what is her
mass?
#6
• During a football game, a receiver has just caught a
pass and is standing still. Before he can move, a
tackler, running at a velocity of +3.9 m/s, grabs and
holds onto him so that they move off together with a
velocity of +2.1 m/s. If the mass of the tackler
is 110 kg, determine the mass of the receiver. Assume
momentum is conserved.
#7
• When a golfer tees off, the head of her golf club which
has a mass of 200 g is traveling 52 m/s just before it
strikes a 46-g golf ball at rest on a tee. Immediately
after the collision, the club head continues to travel in
the same direction but at a reduced speed
of 45 m/s. Neglect the mass of the club handle and
determine the speed of the golf ball just after impact.
#8
• A 6.00-g bullet has a muzzle velocity of 220 m/s when
fired by a rifle with a weight of 40.0 N.
(a)Determine the recoil speed of the rifle.
(b)If a marksman with a weight of 700 N holds the rifle
firmly against his shoulder, determine the recoil
speed of the shooter and rifle.
#9
• A man holding a rock sits on a sled that is sliding
across a frozen lake (negligible friction) with a
speed of 0.490 m/s. The total mass of the sled,
man, and rock is 95.0 kg. The mass of the rock
is 0.300 kg and the man can throw it with a
speed of 15.5 m/s. Both speeds are relative to
the ground.
• Determine the speed of the sled if the man
throws the rock forward (i.e. in the direction the
sled is moving).
• Determine the speed of the sled if the man
throws the rock directly backward.
#10
• A cue ball at rest on a frictionless pool table is hit dead
center by a pool stick, giving it an impulse
of +1.15 N · s. The ball slides (the combination of
hitting the ball dead center and no friction allows this
to happen) along the table and makes a head-on
elastic collision with another pool ball. If both pool
balls have a mass of 0.166 kg, determine the velocity
of the second ball the instant after the collision.
Answers
1. 0.771 m
2. 0.27 kg
3. A) 24 N·s
7. 30.4 m/s
8. A) 0.323 m/s
B) 19.2 m/s
C) 17.7 m/s
9. A) 0.442 m/s
4. A) 188 kg m/s
B) 1.58 m/s
5. 35.9 kg
6. 94.3 kg
B) 0.0175 m/s
B) 0.541 m/s
10. 6.93 m/s