Your Name: _______________________ PHY203

Exam #2

Student ID: ________________________ Chapters 4-7

Thurs., 10/23/03

Lecture Time: 9 a.m 1p.m. 2p.m. 3p.m. Honors

Score = 4 x (25 - ______)

Your Name: _______________________ PHY203

Exam #2

Student ID: ________________________ Chapters 4-7

Thurs., 10/23/03

1. A block is pulled along a frictionless surface with a horizontal force of 10N. The acceleration of the block is 2.5 m/s². Calculate the mass of the block:

a. 4.0 kg

b. 0.25 kg

c. 0.40 kg

d. 25.0 kg

e. 40.0 kg

2. A block is pulled along on a frictionless surface with a horizontal pulling force of 10N for a distance of 2m. Calculate the work done:

a. 20 J

b. 5 J

c. 50 J

d. 2 J

e. 200 J

3. A block is pulled horizontally along on a frictionless surface with a pulling force of 10N at an angle of 60 degrees with respect to the horizontal for a distance of 2m. Calculate the work done:

a. 5J

b. 10 J

c. 20 J

d. 40 J

e. 2.5 J

4. A particle of m=2 kg undergoes a displacement of d = -3mi + 6 mj. During the displacement, a constant force, F = 5Ni + 10Nj, acts on the particle. Calculate the work done by the force:

a. 0 J

b. 45 J

c. 75 J

d. -45 J

e. -75 J

5. A block is pulled along on a frictionless surface for 2 minutes causing an expenditure of 60J. Calculate the average power during this time:

a. 0.50 W

b. 30 W

c. 60 W

d. 120 W

e. 7200 W

6. A 5 kg block is traveling along on a frictionless surface with an initial velocity of 10 m/s. 50J of work is applied to the block. Calculate the final velocity:

a. 4.5 m/s

b. 8.9 m/s

c. 10.5 m/s

d. 11.0 m/s

e. 12.3 m/s

7. A block of mass 5 kg is attached to a spring and sitting on a horizontal frictionless surface. With a spring extension of 20 cm, the energy stored in the spring is 40J. Calculate the spring constant of the spring:

a. 0.2 N/m

b. 2.0 N/m

c. 20 N/m

d. 200 N/m

e. 2000 N/m

8. A block of mass 2 kg is accelerated from 10 m/s initial velocity by a pulling force on a horizontal frictionless surface. After 2m the velocity of the block is 15 m/s. Calculate the magnitude of the force:

a. 31.3 N

b. 62.5 N

c. 112.5 N

d. 125 N

e. 250 N

(For problems 9-12)

A sphere of mass, m= 2 kg, attached to a string is turning in a vertical circle with radius, r = 0.5 m. At the top of the circle, the particle has a kinetic energy of K = 50J.

9. Calculate the speed of the sphere at the top of the circle:

a. 5.0 m/s

b. 7.1 m/s

c. 10.0 m/s

d. 14.1 m/s

e. 25.0 m/s

10. Calculate the tension, T, in the string at the top of the circle:

a. 80.4 N

b. 119.6 N

c. 180.4 N

d. 200.0 N

e. 220.0 N

11. Calculate the potential energy of the sphere at the top of the circle, taking the origin of the potential

energy as the center of the circle:

a. 0 J

b. 4.9 J

c. 9.8 J

d. 19.6 J

e. 39.2 J

12. Calculate the kinetic energy of the sphere at the bottom of the circle:

a. 30.4 J

b. 40.2 J

c. 59.8 J

d. 69.6 J

e. 89.2 J
(For problems 13-14)

Two blocks, (m₁ =20 kg and m₂ =10kg) are pushed with a horizontal external applied force,

F = 100N, as shown below. Assume a frictionless surface.

13. Calculate the (same) acceleration of the blocks:

a. 0 m/s²

b. 3.33 m/s²

c. 5.0 m/s²

d. 6.67 m/s²

e. 10.0 m/s²

14. Calculate the magnitude of the contact force between the blocks:

a. 5.0 N

b. 10.0 N

c. 33.3 N

d. 66.7 N

e. 100 N

(For problems 15-17)

A block of mass 5.0 kg. is released on the ramp below and slides 2 meters down a 30^o ramp.

15. Calculate the potential energy of the block before it is released, taking the origin of the potential

energy at the base of the ramp:

a. 24.5 J

b. 42.5 J

c. 49.0 J

d. 85.0 J

e. 98.0 J

16. Assuming a frictionless ramp, calculate the velocity of the block after it has traveled to the bottom of

the ramp:

a. 3.13 m/s

b. 4.12 m/s

c. 4.43 m/s

d. 5.83 m/s

e. 6.26 m/s

17. If the ramp is in fact rough with a kinetic friction coefficient of m_k = 0.25, calculate the energy converted

by friction to heat by the block sliding down the ramp:

a. 10.6 J

b. 12.3 J

c. 21.2 J

d. 24.5 J

e. 42.2 J

(For problems 18-21)

A block of mass m=5 kg is attached to a spring with spring constant, k = 200 N/m, and hangs down so that it rests on a table as shown below. This causes the spring to stretch by 10 cm from its equilibrium length. Assume the static coefficient of friction between the table and block is 0.6. An external force, F, is applied in the positive x-direction, as shown.

18. Calculate the force on the block due to the stretched spring:

a. 2.0 N

b. 20.0 N

c. 69.0 N

d. 200 N

e. 2000 N

19. Calculate the normal force on the block:

a. 9.0 N

b. 29.0 N

c. 49.0 N

d. 69.0 N

e. 89.0 N

20. What is the direction of the static frictional force:

a. there is none

b. +x

c. -x

d. +y

e. -y

21. Calculate maximum force, F, that can be applied to the block such that the block will continue to remain at rest:

a. 5.4 N

b. 17.4 N

c. 29.4 N

d. 41.4 N

e. 53.4 N

(For problems 22-25)

A person with mass M = 50 kg is standing on a scale in an elevator.

22. If the elevator is not moving, calculate the scale reading:

a. 0 N

b. 50 N

c. 240 N

d. 490 N

e. 740 N

23. If the elevator is traveling upward with a constant velocity of 10 m/s, calculate the scale reading:

a. 0 N

b. 9.5 N

c. 240 N

d. 490 N

e. 990 N

24. If the elevator is accelerating upward with an acceleration of 10 m/s², calculate the scale reading:

a. 0 N

b. 9.5 N

c. 240 N

d. 490 N

e. 990 N

25. If the elevator is traveling upward with an initial velocity of 10 m/s, but is slowing down at a rate of

2 m/s², calculate the scale reading:

a. 9.5 N

b. 390 N

c. 490 N

d. 590 N

e. 990 N

PHY203

Exam #2, F/03

Crib Sheet

Chapters 4-7

(Note: Use 9.81 m/s2 for g, the acceleration due to gravity.)

For constant acceleration(in one dimension):

x_f = x_o + v_ot + (1/2)at2

v_f = v_o + at

v_f2 = v_o2 + 2a(x_f - x_o)

(Note: Bold letters indicate vectors below.)

F = ma

spring force: F = -kDx , where k is the spring constant

weight: W = mg

friction force:

kinetic fk = mkFn , where Fn is the normal force and mk is

the kinetic frictional coefficient

static fs < msFn, fsmax = msFn

uniform circular motion

centripetal acceleration: a = v2/R

Work and Energy

W = F ^. d = Fdcosq

Work done by friction = -f_kDs

E_Thermal = |Work done by friction|

Kinetic Energy: K = (1/2)mv²

Potential Energy: U_spring = (1/2)kx²

U_grav = mgh

Total energy, E, is conserved ( a constant).

Power = Work/Time