PHYSICS 231
1st Midterm, October 11, 1996, 5:30 pm - 6:30 pm
Instructor: P. Q. Hung

Do all problems (25 points each). READ them carefully. You have to EXPLAIN all your answers. DO NOT just write them down. ANSWERS WITHOUT EXPLANATION WILL BE GIVEN NO CREDIT.

Useful formulas:

I) A baseball is thrown toward a player with an initial speed of 20 m/s at an angle of with the horizontal. At the moment the ball is thrown, the player is 50 m from the thrower. At what speed and in what direction must the player run to catch the ball at the same height at which it was released?

The ball reaches the player at an x distance of

.

We can find the time it takes the ball to reach the player by

.

The player therefore has to run 50-40.82=9.18m in 2.886 seconds.

(toward the thrower)

II) A body of mass 0.12 kg that can move only in the x-y plane is at rest at the origin of the x-y coordinate system at time t=0 s. Two constant forces and act on the body. (a) Draw the force diagram for the body. (b) What are the position and velocity vectors of the body at time t= 2 s?

a)

b)