Past Exam 2

Question 1

a merry-go-around of radius 2 m and moment of inertia 100 kg m^2 is initially at rest. a kid of mass 40 kg is running tangentially to the perimeter of the merry-go-round at a speed of 2 m/s, and jumps on. what is the rotational velocity of the merry-go-round with the kid on it?

Answer 1

0.62 rad/s

Question 2

a 80 kg hiker climbs a mountain in 8 hours. if the climber’s vertical elevation increases 3.6 km, what is the average power of the process needed for the increase in gravitational energy?

Answer 2

98 W

Question 3

an ideal gas takes up 600 cm^3 of volume at a temperature of 25 degrees Celsius. At what temperature will this same gas occupy 1150 cm^3 if the pressure is held constant?

Answer 3

298 degrees Celsius

Question 4

a 2 m long horizontal uniform beam of mass 20 kg is supported by a wire as shown in the figure. the wire makes an angle of 20 degrees with the beam. attached to the beam, 1.40 m from the wall, is a ball with a mass of 40 kg.

Answer 4

1090 N

Question 5

a person who weighs 100 kg hops onto a rowing boat. the boat sinks an additional 2 cm deeper into thee water. what is the cross-sectional area of the boat? assume the seawater density is 1000 kg/m^3.

Answer 5

5 m^2

Question 6

a 3 kg hollow sphere of radius 5 cm starts from rest and rolls without slipping down a 15 degree incline. if the length of the incline is 100 cm, then the velocity of the center of mass of the hollow sphere at the bottom of the incline is:

Answer 6

1.75 m/s

Question 7

a flywheel has a rotational inertia of I = 1000 kg m^2. it is initially rotating at 1000 rpm. you want to stop the wheel in 60 sec. what is the resistive torque must you supply?

Answer 7

1750 N*m

Question 8

a 10 kg piece of aluminum sits at the bottom of a lake, right next to a 10 kg piece of lead, which is much denser than aluminum. which one has the greater buoyant force on it?

Answer 8

the aluminum

Question 9

a large block is attached to a spring scale which measures a weight of 250 N. the block is then completely submerged in water, which has a density of 1000 kg/m^3. the spring scale then reads 200 N.

Answer 9

.005 m^3

Question 10

a 1200 kg car is traveling at 3 m/s and strikes a wall. the car bounces off the wall with a velocity of 4 m/s. if the contact with the wall by the car lasts for 0.10 seconds, then the average force on the car is:

Answer 10

84,000 N

Question 11

two carts are involved in an inelastic collision. cart A with a mass 1 kg hits cart B with a mass 0.5 kg. the two carts stick together after the collision and continue to move along together. cart A has an initial velocity of 2 m/s and cart B is initially at rest. what is the final velocity of the two-cart system?

Answer 11

1.3 m/s

Question 12

a pulley with radius 0.2 m and mass M = 1.5 kg is attached to a falling bucket with mass M = 1.5 kg. what will be the linear acceleration of the falling bucket after it is released? model the pulley as a uniform disk.

Answer 12

6.5 m/s^2

Question 13

a 30 cm wrench is used to generate a torque at a bolt. a force of 50 N is applied at the end of the wrench at an angle of 70 degrees. the torque generated at the bolt is:

Answer 13

14.1 N*m

Question 14

how many moles are there in 2 kg of copper? the atomic weight of copper is 63.5 g/mol and its density is 8.90 g/cm^3

Answer 14

31.5

Question 15

an ice dancer with her arms stretched out starts into a spin with an angular velocity of 1 rad/s. her moment of inertia with her arms stretched out is 2.48 kgm^2. what is the increase in her rotational kinetic energy when she pulls in her arms to make her moment of inertia 1.40 kgm^2

Answer 15

0.957 J

Question 16

a submarine is at a depth of 500 m under the water. the force on a circular hatch of 1 m in diameter due to the seawater (density = 1025 kg/m^3) pressure from outside the submarine is:

Answer 16

3.95 x 10^6 N

Question 17

what buoyant force does a 0.50 kg solid gold crown experience when it is immersed in water? the density of gold is 19.3 x 10^3 kg/m^3 and that of water is 1000 kg/m^3.

Answer 17

0.25 N

Question 18

in any collision:

Answer 18

total momentum is conserved

Question 19

the pressure in a bottle is 40 PSI at room temperature (20 degrees Celsius). the bottle temperature is slowly increased to 90 degrees Celsius. what is the pressure in the bottle at 90 degrees Celsius.

Answer 19

50 PSI

Question 20

a person sits on a freely spinning lab stool that has no friction in its axle. the person is spun around by a friend. when this person extends her arms while spinning :

Answer 20

her moment of inertia increases and her angular speed decreases

Question 21

A styrofoam block of volume 1m^3 is flowing in water (density 1x10^3kg/m^3)… assuming the block is fully submerged in water, what is the buoyancy force acting on the blocks?

Answer 21

9.8kN

Question 22

if h=1m, the length of each cable is I=2m, and the mass is 100kg, what is the tension T in each cable?

Answer 22

980N