For solutions , schedules, and sample midterms visit : http://usapes2.people.uic.edu/current.html
Warm up: 6 min.
1a Object is released from rest at height h. What is the velocity when it reaches the Earth. 1b Find work done by the
force due to gravity. (no friction due to air)
2a Object is thrown straight up with initial velocity V0. What max height can it reach? 2bFind work done by the force due
to gravity.(no friction due to air)
3 What is potential energy of the object at height 5m from the ground ? Does this question make any sense? Expand
your answer.
Warm up: 8 min
4 A massless, rigid rod is a length L. Its top is pivoted on a frictionless horizontal axle. The rod hangs straight down at rest
with a small, steel ball of mass m attached to it bottom end. You strike the ball, suddenly giving a horizontal velocity vi so
that it can just swing around in a full circle. What minimum speed at the bottom is required to make the ball go over the
top of the circle? Ans vi= 2 * Sqrt(gL)
5. A block of mas m = 4.00 kg is attached to a spring of force constant k = 400.0 N/m as shown in the figure below. The
block is pulled to a position xi = 4.00 cm to the right of equilibrium and released from rest. The coefficient of kinetic
friction between the block and surface is 0.125. As the block passes the equilibrium point of the spring, use energy
analysis to find the speed of the block. Ans: vf = 0.249 m/s
Problem set:
1 Two marbles (m1 = 1/3 m2) collide head on. Marble #1 enters the collision with a velocity of 4.00 m/s to the right.
Marble #2 enters the collision with a velocity of 4.00 m/s to the left. If the collision is perfectly elastic, what are the final
velocities for the balls? Ans: v1f = -8 m/s ; v2f = 0 m/s
2. One afternoon, while their parents weren’t paying attention, Benjamin convinces his younger and more
impressionable sister Evelyn that they should recreate William Tell’s apple shot. Instead of bow and arrow, though,
Benjamin will be using his new slingshot ( a present from his uncle) to hit an apple placed on Evelyn’s head.Dont’t worry,
though, Evelyn has a laboratory – grade face shield ( a gift from her aunt, who thought of such an eventuality) to wear
during the event. If the pebble (mp=20.0 g) fired from the slingshot hits the apple (ma=230 g ) with a velocity of 30.0 m/s
in the horizontal direction and embeds itself in the apple, how far does the apple travel horizontally before hitting the
ground? Evelyn is 1.0 m tall, and you can ignore friction between the apple and Evelyn’s head. Ans: 1.08 m
3. A 15-g bullet is fired horizontally into a 3-kg block of wood suspended by a long cord. The bullet sticks in the block.
Compute the velocity of the bullet if the impact causes the block to swing 10 cm above its initial level. Ans vb= 281
m/s(Hint decompose the problem into subproblems)