Momentum

Chapter 9; Linear Momentum and Collisions

| ToC, Chapter 9 | Course Calendar |

D9.1 What is the momentum of a 1200 kg sedan traveling at 90 km/hr? At what speed must a 3600 kg truck travel to have the same momentum?

D9.2 A 150 gram baseball initially traveling at 30 m/s is struck by a bat and leaves in the opposite direction at 35 m/s.

a) What is its change in momentum?
b) Is the change in momentum directed along the initial velocity, the final velocity, or some other direction?
c) What is the impulse delivered by the bat?
d) In hitting a baseball, why is it important to "follow through," that is, keep the bat moving and make a full swing, rather than to stop right after the ball is hit?

D9.3 A 600 kg cannon fires a 5 kg cannonball with a horizontal muzzle velocity of 120 m/s. What is the recoil velocity of the cannon?

D9.4 An astronaut of mass 105 kg carrying an empty oxygen tank of mass 40 kg is stationary relative to a nearby space shuttle. She throws the tank away from herself with a speed of 2 m/s (measured relative to the shuttle). With what velocity relative to the shuttle does the astronaut start to move through space?

D9.5 A 10 000 kg railroad grain car and its load of 3 000 kg of grain coast along a level track at 3.0 m/s. A door is open slightly and lets the grain pour out at a rate of 100 kg/s. What is the speed of the grain car after the grain has all emptied from the car? What has happened to the initial kinetic energy of the railroad car?

D9.6 An inflated rubber raft of mass 30 kg carries two swimmers of mass 50 kg and 70 kg. The raft and swimmers are initially floating at rest when the swimmers simultaneously dive off from the mid-points of opposite ends of the raft, each with a horizontal velocity of 3 m/s. The 50 kg swimmer dives to the left; the 70 kg swimmer dives to the right. With what speed and in what direction does the raft start to move?

D9.7 A 600 g glider sits at rest on an air track when it is struck by a 250 g glider traveling at 25 cm/s. The two couple and stick together. What is their velocity?

D9.8 A 25 g bullet is fired horizontally with a speed of 100 m/s into a 5.0 kg block of wood; the wooden block and bullet start to move off with speed v_f. What is this speed v_f? The block is suspended by cords so that it moves in an arc (but does not rotate) as is illustrated in the figure. What is the height h to which it rises?

D9.9 A stationary ²³⁸U nucleus with atomic mass 238 x 1.67 x 10^-27 kg decays by emitting an alpha particle with atomic mass 4 x 1.67 x 10^-27 kg at a speed of 1.5 x 10⁷ m/s. What will be the recoil velocity of the resulting ²³⁴Th nucleus?

D9.9 A 600 g glider moves on an air track with a velocity of 10 cm/s to the right while a 400 g glider moves to the left with a velocity of 20 cm/s. The two collide elastically. What is the velocity of each after the collison?

D9.10 Below are eight sets of initial conditions for perfectly elastic collisions on an air track. Glider number two is at rest in each case. Calculate the velocity of glider number two in each case and rank them in order of increasing velocity of glider number one.

	mass of glider #1	velocity of glider #1	mass of glider #2	velocity of glider #2
A	300 g	10 cm/s	600 g	0
B	300 g	10 cm/s	300 g	0
C	300 g	10 cm/s	200 g	0
D	600 g	15 cm/s	200 g	0
E	600 g	20 cm/s	250 g	0
F	300 g	25 cm/s	350 g	0
G	250 g	28 cm/s	375 g	0
H	375 g	28 cm/s	250 g	0

D9.11 Exhaust gases leave a certain rocket with a speed of 300 m/s. What must be the mass flow rate in order to lift the 50 000 kg rocket?
F_thrust = u = M g = W t
=
=
= 1,633

| ToC, Chapter 9 | Course Calendar |