Q: Which of the following is the impulse-momentum theorem for linear motion?

$$F_{\text{net}} \Delta t = m \Delta v = \Delta p$$

Question 1

A 2.0 kg clay ball moving at 3.0 m/s collides with a stationary 1.0 kg clay ball on a frictionless surface. If the balls stick together after the collision, what is their final velocity?

Accepted Answer

$$2.0\ \mathrm{m/s}$$

Question 2

Which of the following best describes a perfectly inelastic collision?

Accepted Answer

The colliding objects stick together and move with a common final velocity.

Question 3

Two railroad cars, one of mass $$2.0 	imes 10^4$\ \mathrm{kg}$$ moving at $$1.5\ \mathrm{m/s}$$ and another of mass $$4.0 	imes 10^4$\ \mathrm{kg}$$ moving in the opposite direction, couple together after collision and move at $$-0.25\ \mathrm{m/s}. $$What was the initial velocity of the heavier car?

Accepted Answer

$$1.1\ \mathrm{m/s}$$

Question 4

In a two-dimensional collision, which of the following must be conserved?

Accepted Answer

Both the x- and y-components of momentum

Question 5

A peregrine falcon of mass $$0.80\ \mathrm{kg}$$ swoops down at $$18.0\ \mathrm{m/s} at a$$ $$45^\circ$$ angle and grabs a $$0.36\ \mathrm{kg}$$ pigeon flying horizontally at $$9.0\ \mathrm{m/s}. $$What is the speed of the combined birds immediately after the collision?

Accepted Answer

$$15\ \mathrm{m/s}$$

Question 6

Which equation correctly expresses the law of conservation of momentum for an isolated system?

Accepted Answer

$$\vec{P}_f = \vec{P}_i$$

Question 7

A merry-go-round of mass $$200\ \mathrm{kg}$$ and radius $$2.0\ \mathrm{m}$$ rotates once every $$2.5\ \mathrm{s}. A$$ $$36\ \mathrm{kg}$$ child walks from the center to the edge. What happens to the rotational period?

Accepted Answer

It increases

Question 8

Which formula gives the angular momentum $$L of a $$rotating object with moment of inertia $$I$$ and angular velocity $$\omega$$?

Accepted Answer

$$L = I \omega$$

Question 9

A spinning ice skater pulls in her arms, reducing her moment of inertia by a factor of 4. If her initial angular velocity was $$2\ \mathrm{rad/s}$$, what is her final angular velocity?

Accepted Answer

$$8\ \mathrm{rad/s}$$

Question 10

Which statement about conservation of angular momentum is correct?

Accepted Answer

Angular momentum is conserved only if no net external torque acts on the system.

Question 11

A cyclist rides a bike with wheels of radius $$0.33\ \mathrm{m}$$ and mass $$1.5\ \mathrm{kg}$$ each at $$10\ \mathrm{m/s}. $$Treating the wheels as hoops, what is the angular momentum of one wheel?

Accepted Answer

$$L = m v r = (1.5)(10)(0.33) = 4.95\ \mathrm{kg\cdot m^2$/s}$$

Question 12

Which of the following is the impulse-momentum theorem for linear motion?

Accepted Answer

$$F_{	ext{net}} \Delta t = m \Delta v = \Delta p$$

Question 13

In a two-dimensional collision, a $$0.80\ \mathrm{kg}$$ falcon moving at $$18.0\ \mathrm{m/s} at$$ $$45^\circ$$ below the horizontal collides with a $$0.36\ \mathrm{kg}$$ pigeon moving horizontally at $$9.0\ \mathrm{m/s}. $$What is the direction of the combined velocity after collision?

Accepted Answer

$$37^\circ$$ below the horizontal

Question 14

If the net external torque on a system is zero, which equation describes the conservation of angular momentum?

Accepted Answer

$$I_i \omega_i = I_f \omega_f$$

Question 15

A $$36\ \mathrm{kg}$$ child stands at the center of a $$200\ \mathrm{kg}$$ merry-go-round (radius $$2.0\ \mathrm{m}) $$rotating every $$2.5\ \mathrm{s}. $$When the child walks to the edge, what is the new period?

Accepted Answer

$$3.4\ \mathrm{s}$$

Question 16

Which of the following is NOT a requirement for using conservation of momentum in a collision problem?

Accepted Answer

The objects must have equal mass.

Question 17

Which of the following statements about impulse is correct?

Accepted Answer

Impulse is the area under the force vs. time curve.

Question 18

A bullet of mass $$0.01\ \mathrm{kg}$$ traveling at $$400\ \mathrm{m/s}$$ embeds itself in a stationary block of mass $$2.0\ \mathrm{kg}. $$What is the final velocity of the block and bullet?

Accepted Answer

$$2.0\ \mathrm{m/s}$$

Momentum, Impulse, and Collisions (Sections 9.5–9.7): Study Notes for Physics for Life Sciences Lecture 15

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