University of California Irvine Angular Velocity and Kinetic Energy Questions 12 questions The following questions should be explained in 3-5 lines: (a) | Course Hero

University of California Irvine Angular Velocity and Kinetic Energy Questions 12 questions

The following questions should be explained in 3-5 lines:

(a) A plane and a fly have the same kinetic energy. Which one has

the greater momentum?

(b) Tug-of-war is played on a frictionless surface between two contes-

tants. Contestant A is much stronger than contestant B. B weighs

80 kgs and A weighs 65 kgs. Determine who loses this contest.

2. Two masses m1 and m2 are at rest on a frictionless surface. They

are connected by a stretched spring and released at time t = 0 as shown in Fig. 1. Calculate the ratio of their speeds, v1 and v2, and

the ratio of their kinetic energies.

Figure 1: Problem 2

3. Two particles collide elastically as one approaches the other di-

rectly from the rear. Particle A has a mass of 42 kg and particle

B 49 kg. If A approaches at 7.50 m/s and car B is moving at 4.60

m/s. Calculate their velocities after the collision.

4. A mass m = 2 kg slides down a ? = 60? inclined plane from a

height of 6 m. At the bottom of the incline, it collides with ano Physics 1A: Homework #4
Assigned: July 14th, 2020
Due: Tuesday, July 21th, 2020, by 11:00 pm, on Gradescope
1. The following questions should be explained in 3-5 lines:
(a) A plane and a fly have the same kinetic energy. Which one has
the greater momentum?
(b) Tug-of-war is played on a frictionless surface between two contestants. Contestant A is much stronger than contestant B. B weighs
80 kgs and A weighs 65 kgs. Determine who loses this contest.
2. Two masses m1 and m2 are at rest on a frictionless surface. They
are connected by a stretched spring and released at time t = 0 as
shown in Fig. 1. Calculate the ratio of their speeds, v1 and v2, and
the ratio of their kinetic energies.
Figure 1: Problem 2
3. Two particles collide elastically as one approaches the other directly from the rear. Particle A has a mass of 42 kg and particle
B 49 kg. If A approaches at 7.50 m/s and car B is moving at 4.60
m/s. Calculate their velocities after the collision.
4. A mass m = 2 kg slides down a ? = 60? inclined plane from a
height of 6 m. At the bottom of the incline, it collides with another
1
mass M = 5 kg, and the latter is initially at rest as shown in Fig.
2. The surface past the incline is horizontal and frictionless. Determine the speeds of the masses after collsion and how far back up
the inclined plane m travels.
Figure 2: Problem 4
5. Impact effects on different objects are tested by smashing heavy
objects into fixed barriers at 18 m/s. An object of mass 3000 lbs
takes 0.1 s from the time of impact until it is brought to rest.
(a) Find the force (on average) exerted on the object by the barrier.
(b) Determine the deceleration of the object.
6. You are given two forces F1 = 60 N and F2 = 4N. Which one
exerts a greater torque. Explain your answer in under three lines.
7. An flywheel slows down from 3000 rpm to 1000 rpm in 2.75 s.
Calculate the following quantities:
(a) its angular acceleration.
(b) the number of revolutions tmade in this time.
8. A boy of mass 100 lbs stands at the center of a rotating merrygo-round (MGR) in th shape of a disk of radius 4 m and mass 20
kg. The platform rotates at ? = 0.76 rad/s. At this moment the
bout walks to the edge of the platform.
(a) Determine the angular velocity of the system (boy + MGR)
when the boy reaches the rim.
(b) Additionally, find the rotational kinetic energy of the system.
9. Consider the diagram of a heart-shaped body as shown in Fig. 3.
2
Calculate the net torque on the body about the point O. Express
your final answer in SI units.
Figure 3: Problem 9
10. A wheel is accelerated from rest at a rate of 2.2m/s2 .
(a) How fast will the point at the top of the wheel be moving after
3.1 s?
(b) Now consider the same wheel as part of bicycle moving on the
road. Given that the velocity of the lowest point of the wheel is zero
at any given time, find the velocity of the top of the wheel.
Figure 4: Problem 11
11. A mass m1 = 1kg is attached to the end of a string and revolves
in a circle on a frictionless surface. The other end of the string
3
passes through a hole in the table and is attached to a mass m2 kg
as shown in Fig. 4. m1 revolves with a constant speed v1i = 2 m/s
in a circle of radius r1 = 0.5 m. If the mass m2 is slowly increased
m2 = 1.6 kg, what is the final speed, v1f , of the mass m1 ?
12. An 220 lb football player is stopped in 1.5 s by a tackle. Find
the average power is required to stop him if he was originally moving
at 4.5m/s.
4

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