Your Name: _______________________ PHY203

Exam #2

Student ID: ________________________ Chapters 4,5

Thurs.,10/12/00

Lecture Section: 9 1 2 3

1. An external force, F, of magnitude 10N is applied to a 20kg block at an angle of 30o with respect to the horizontal, as shown below. Assume the surface under the mass is frictionless.

a. Redraw the block and draw in all the forces on the block (free body diagram)

b. Calculate the x-component and y-components of the applied force (including the correct signs), using the coordinate system shown in the figure.

c. Calculate the normal force, FN, (including the correct sign).

d. Calculate the acceleration of the block (including the correct sign).

e. Calculate how far the block will travel from rest in a time of 10 s.

2. A block of mass 5 kg is attached to a spring with spring constant, k = 500 N/m, and swung with constant velocity in a circle of radius 1 m on a horizontal, frictionless table. Assume this causes the spring to stretch by 10 cm from its equilibrium length (which is 90 cm to give a total radius of 1 m).

a. Calculate the centripetal force exerted by the spring on the block.

b. Calculate the centripetal acceleration of the block.

c. Calculate the speed of the block.

3. Two blocks, one of steel (mass =20 kg, mk = 0.6) and one of

brass (mass =10kg, mk= 0.4) are pulled with a horizontal external applied force, F, of magnitude 400N on a steel table, as shown below, so the blocks accelerate in the +x direction. A string with tension, T, connects the two blocks. Assume there are frictional forces between the blocks and the table.

a. Redraw the blocks and sketch all of the forces on each block (free body diagrams).

b. Calculate the normal forces, FN, on the steel and brass blocks (including the correct signs), using the coordinate system given in the figure.

c. Calculate the frictional forces, f, on the steel and brass blocks.

(Problem 3 is continued on the next page)

d. Calculate the tension in the string and the (same) acceleration of the two blocks.

PHY203

Exam #2

Crib Sheet

Chapters 4,5

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

Constant acceleration:

xf = xo + vot + (1/2)at2

vf = vo + at

Vf2 = vo2 + 2a(xf - xo)

(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 force: F = mv2/r

centripetal acceleration: a = v2/r

period: T = 2pr/v