Physics Unit F
Two ice skaters push off against one another starting from a stationary position. The 45-kg skater acquires a speed of 0.375 m/s. What speed does the 60-kg skater acquire?
0.281 m/s
A 0.140-kg baseball is dropped and reaches a speed of 1.20 m/s just before it hits the ground. It rebounds with a speed of 1.00 m/s. What is the change of the ball's momentum?
0.308 kg∙m/s upwards
A 0.140-kg baseball is dropped from rest from a height of 2.00 m above the ground. What is the magnitude of its momentum just before it hits the ground?
0.877 kg∙m/s
A firecracker breaks up into two pieces, one has a mass of 200 g and flies off along the x-axis with a speed of 82.0 m/s and the second has a mass of 300 g and flies off along the y-axis with a speed of 45.0 m/s. What is the total momentum of the two pieces?
21.2 kg∙m/s at 39.5° from the x-axis
A 500-kg cannon fires a 4.0-kg projectile with a velocity of 500 m/s relative to the ground. What is the recoil speed of the cannon?
4.0 m/s
A golf club exerts an average force of 1000 N on a 0.045-kg golf ball which is initially at rest. The club is in contact with the ball for 1.8 ms. What is the speed of the golf ball as it leaves the tee?
40 m/s
A 900-kg car traveling east at 15.0 m/s collides with a 750-kg car traveling north at 20.0 m/s. The cars stick together. In what direction does the wreckage move just after the collision?
48.0° N of E
A 2.00-g bullet hits and becomes embedded in a 5.00-kg wood block which is hanging from a 1.20-m long string. This causes the block to swing through an arc of 3.50°. What was the speed of the bullet before it hit the block?
524 m/s
An elastic collision of two objects is characterized by the following.
Both A and B are true. Total momentum of the system is conserved. Total kinetic energy of the system remains constant.
When objects stick together after colliding, the collision is completely elastic.
False A perfectly inelastic collision occurs when the maximum amount of kinetic energy of a system is lost. In a perfectly inelastic collision, i.e., a zero coefficient of restitution, the colliding particles stick together. In such a collision, kinetic energy is lost by bonding the two bodies together
The impulse delivered to an object is equal to the change in the object's velocity.
False I=Fnet*DeltaT F=m(a)=m(DeltaV/DeltaT) I=m(DeltaV/DeltaT)*DeltaT I=m*DeltaV
A system that has zero momentum must also have zero kinetic energy
False In a system there is conservation of momentum, so the total momentum will not change Kinetic Energy can be lost in a system so there is no conservation if it's an Inelastic Collusion
Internal forces cannot change the total kinetic energy of a system.
False Yes cause in Inelastic Collison, Kinetic Energy can be lost from the system Ki > Kf
A freight car moves along a frictionless level railroad track at constant speed. The freight car is open on top. A large load of coal is suddenly dumped into the car. What happens to the speed of the freight car?
It decreases. Conserv. of P: Pi=Pf p1i+ p2i =p1f +p2f mv0+ 0 = mv + (m/2)v v= mv0/ (3m/2) = 2v0 / 3
A ping-pong ball moving east at a speed of 4 m/s, collides with a stationary bowling ball. The Ping-Pong ball bounces back to the west, and the bowling ball moves very slowly to the east. Which object experiences the greater magnitude impulse during the collision?
Neither; both experienced the same magnitude impulse. In a collision, impulse is met with an equal and opposite reaction Newton's Third Law I=F*time
An artillery shell explodes in midair and breaks up into many fragments. Which of the following statements are true regarding conditions immediately before and immediately after the explosion: ----- I. The total momentum of the fragments is equal to the original momentum of the shell. ----- II. The total kinetic energy of the fragments is equal to the original kinetic energy of the shell.
Statement I only Conservation of Momentum Total System has a constant Momentum Kinetic Energy is not Conserved in an Inelastic Collision (Permanent Deformation)
Jacques and George meet in the middle of a lake while paddling in their canoes. They come to a complete stop and talk for a while. When they are ready to leave, Jacques pushes George's canoe with a force F to separate the two canoes. What is correct to say about the final momentum and kinetic energy of the system?
The final momentum is zero kg∙m/s but the final kinetic energy is positive Conservation of Momentum Kinetic Energy is positive because the canoes are in motion.
An object that is initially at rest breaks up into two pieces of unequal masses when a spring-loaded device is released. If you compare the kinetic energy of the larger mass to that of the smaller mass immediately after they separate, which of the following statements is correct?
The kinetic energy of the smaller mass is greater. the smaller mass experiences a greater change in velocity
A tennis ball undergoes an elastic collision when it hits the ground and bounces up. It is given that the speed of the ball just before it hits the ground is -v0 and immediately after rebounding it is +v0 . Which of the statements below is true?
The momentum of the ball changes and the momentum of Earth also changes by the same amount. equal changes of momentum conservation of momentum
In a collision between two unequal masses, how does the impulse imparted to the smaller mass by the larger mass compare with the impulse imparted to the larger mass by the smaller one?
They are equal. In a collision, impulse is met with an equal and opposite reaction Newton's Third Law I=F*time
An inelastic collision of two objects is characterized by the following
Total momentum of the system is conserved. Inelastic collision-only momentum is conserved. Pi= Pf & Kf< Ki
Internal forces cannot change the total momentum of a system.
True Conservation of Momentum of the System Individual Object's change their momentum, but total momentum is constant
The center of mass of an object does not have to be located within the object.
True In the case of a single rigid body, the center of mass is fixed in relation to the body, and if the body has uniform density, it will be located at the centroid. The center of mass may be located outside the physical body, as is sometimes the case for hollow or open-shaped objects, such as a horseshoe.
A particle that has zero momentum must also have zero kinetic energy.
True P = m*v K = 1/2 m*v^2 Mass is never 0 so if v=0, then both are 0
The net force acting on an object is equal to the rate of change of its momentum.
True P = mv = I I = Fnet*DeltaT Fnet = P/DeltaT
In a one-dimensional elastic collision of two identical masses, the masses exchange velocities.
True This question is asking about 1 particle. If it refers to a system of multiple objects, the statement will be false.
Identical forces act for the same length of time on two different masses. The change in momentum of the smaller mass is
equal to the change in momentum of the larger mass. Objects in a system experience and equal yet opposite in direction change in momentum
A rope is lying on a table. You pick up one end and start raising it with a constant velocity. The force you have to exert on the rope is
greater than the weight of the portion of the rope that is not on the table. Force needs to be greater than part at rest to raise it
A railroad car of mass m and speed v collides and sticks to an identical railroad car that is initially at rest. After the collision, the kinetic energy of the system
is half as much as before. p1i+ p2i =p1f +p2f m1v1i+ m2v2i=m1v1+ m2v2 mv0+ 0 = mv + mv v= mv0/ 2m = ½v0 Energy loss = DeltaK = Kf-Ki = ½ (2m)(vf)^2 -½ m(v0)^2 = ½ (2m)(v0/2)^2 -½ m(v0)^2 = ½(2m) (v0^2 /4) -Ki = ½mv0^2 ( ½ - 1) = -½K
Two different masses have equal, non-zero kinetic energies. The momentum of the smaller mass is
smaller than the momentum of the larger mass. P=mv < P=Mv
A rubber ball and a lump of putty have equal mass. They are thrown with equal speed against a wall. The ball bounces back with nearly the same speed with which it hit. The putty sticks to the wall. Which objects experiences the greater momentum change?
the ball Momentum has size and direction the ball experienced a greater change as it changed direction away from the wall with equal velocity
A ping-pong ball originally at rest is hit head-on by a bowling ball moving with initial speed v0. It is given that the mass of the ping-pong ball is as good as negligible in comparison with the mass of the bowling ball. What is the speed of the ping-pong ball after this elastic collision?
v2=2v0 m1v1i+m2v2i = m1v1+m2v2 If m1 >> m2 , v1i= v0, v2i= 0 m1v0+0=m1v1+m2v2 v1=(m1-m2)/(m1+m2) * v0 v1=(m1)/(m1) *v0 v2=(2m1/(m1+m2))*v0 = 2v0 v1= v0, v2= 2v0
