PHY 1151
Fall 2002
First Hour Exam -- version 1
September 20, 2002
Rx = Ax + Bx + Cx
Rx = 3 + 5 + 7
Rx = 15
Ry = Ay + By + Cy
Ry = - 4 - 6 + 8
Ry = - 2
Please notice that Question 3 is very similar to "Another Example" from the notes and discussion of Projectile Motion.
The original solution to this problem did NOT correspond to the question.
The question has been changed to correspond to the solution.
4. A 2 kg block sits on a smooth (frictionless) plane inclined 20° above the horizontal. It is connected by a string to a 5 kg mass that hangs suspened from the other end of the string as shown in the sketch above.
a) Draw clear, complete “free-body” diagrams showing all the forces on the two masses.
b) Apply Newton’s Second Law, F = m a, to the two masses and find the acceleration of the system.
First, we apply F = m a to the 5-kg mass:
To get that "more information", we apply F = m a to the 2-kg block on the inclined plane:
a = 6.04 m/s2
T = 6.70 N + (2 kg)(6.04 m/s2)
T = 6.70 N + 12.08 N
T = 18.78 N
