Inelastic Collisions
The firing of a bullet by a rifle causes the rifle to recoil backwards. How does the rifle's recoil speed compare to the bullet's launch speed? (less than, greater than, equal to)
The rifle's recoil speed is LESS than the bullet's launch speed.
[Open reference photo in slides] What is the impulse delivered to the yellow ball during the collision?
-20 kg m/s
True or false: In a collision, the net impulse experienced by an object is equal to its momentum change.
True. By definition, impulse is the change in momentum.
[Open reference photo in slides] Complete the table below.
px=67 kg m/s
py=36 kg m/s
Is momentum a vector or scalar quantity?
Momentum is a vector quantity.
In a physics experiment, two equal-mass carts roll towards each other on a level, low-friction track. One cart rolls rightward at 2 m/s and the other cart rolls leftward at 1 m/s. After the carts collide, they couple (attach together) and roll together. What is their final velocity?
vf=0.5 m/s right
[Open reference photo in slides] What is the final velocity of the blue object after the collision (include direction)? Assume a totally elastic collision.
vf=6 m/s to the right
A -5 N force is applied to a 3 kg ball to change its velocity from +9 m/s to -3 m/s. This impulse causes the momentum change of the ball to be ____ kg•m/s.
-36 kg•m/s
A 1500 kg car is moving to the right with a velocity of 60 m/s and collides with a 750 kg car moving upwards at 18 m/s. They stick together and move as one. What is the y-direction velocity after they collide?
vy=6 m/s upwards
A truck driving along a highway road has a large quantity of momentum. If it moves at the same speed but has twice as much mass, its momentum is ________________. (zero/quadrupled/doubled/unchanged)
A truck driving along a highway road has a large quantity of momentum. If it moves at the same speed but has twice as much mass, its momentum is DOUBLED.
A 46 gram tennis ball is launched from a 1.35 kg homemade cannon. If the cannon recoils with a speed of 2.1 m/s, determine the muzzle speed of the tennis ball.
vmuzzle=61.63 m/s
DAILY DOUBLE!
What is the difference between totally elastic and partially elastic collisions?
Partially elastic collisions do NOT conserve kinetic energy. Totally elastic collisions DO conserve kinetic energy.
A 0.5 kg ball moving at 5 m/s strikes a wall and rebounds in the opposite direction with a speed of 2 m/s. If the impulse occurs for a time duration of 0.01 s, then the average force acting upon the ball is ____ N.
-350 N
A 1.3 kg ball is moving to the right with a velocity of 8 m/s and collides with a 0.2 kg lump of clay moving upwards at 3.7 m/s. They stick together and move as one. What is the x-direction velocity after they collide?
vx=6.93 m/s to the right
When a mass M experiences a velocity change of v in a time of t, it experiences a force of F. Assuming the same velocity change of v, the force experienced by a mass of 2M in a time of (1/2)t is ____.
4F
A 2.8 kg physics cart is moving forward with a speed of 45 cm/s. A 1.9 kg brick is dropped from rest and lands on the cart. The cart and brick move together across the horizontal surface. What is the speed of the cart and brick after they collide?
vf=0.268 m/s
[Open reference photo in slides] Assuming this is a completely elastic collision, determine the final speed of the wall if: mwall=340 kg, mball=78 kg, v0(ball)=50 m/s, and vf(ball)=13 m/s.
vf(wall)=8.49 m/s
A -5 N force is applied to a 3 kg ball to change its velocity from +9 m/s to -3 m/s. The impulse is encountered by the ball for a time of ____ seconds.
7.2 seconds
A 1.9 kg ball is moving to the right with a velocity of 8 m/s and collides with a 0.1 kg lump of clay moving upwards at 5.9 m/s. They stick together and move as one. What is the overall magnitude of their momentum after they collide? (no angle needed)
pf=15.21 kg m/s
DAILY DOUBLE!
An object with a mass M and a velocity v has a momentum of 32 kg•m/s. An object with a mass of 4M and a velocity of 0.75v would have a momentum of ____ kg•m/s.
96 kg•m/s
A 9230-kg truck collides head on with a 1250-kg parked car. The vehicles entangle together and slide a linear distance of 10.6 meters before coming to rest. Assuming a uniform coefficient of friction of 0.820 between the road surface and the vehicles, determine the pre-collision speed of the truck.
v0=14.82 m/s
[Open reference photo in slides] During a partially elastic collision, a two-car system loses 10,000 J of energy in the form of heat and sound. Using the photo as a reference, what is the final speed of the truck?
vf=4.28 m/s
A 3.0 kg object is moving forward with a speed of 6.0 m/s. The object then encounters a force of 2.5 N for 8.0 seconds in the direction of its motion. The object then collides head-on with a wall and heads in the opposite direction with a speed of 5.0 m/s. Determine the impulse delivered by the wall to the object (include +/- direction).
-53 Ns
Two ice skaters collide on the ice. A 39.6 kg skater moving South at 6.21 m/s collides with a 52.1 kg skater moving East at 4.33 m/s. The two skaters entangle and move together across the ice. Determine the magnitude and direction of their post-collision velocity.
vf=3.64 m/s 47.47 deg below the horizontal
A classic physics demonstration involves firing a bullet into a block of wood suspended by strings from the ceiling. The height to which the wood rises below its lowest position is mathematically related to the pre-collision speed of the bullet. If a 9.7 gram bullet is fired into the center of a 1.1-kg block of wood and it rises upward a distance of 33 cm, then what was the pre-collision speed of the bullet?
v0=290.95 m/s