Three blocks of weights W1 = 11 lb, W2 = 9 lb, and W3 = 10 lbare strung in the massless pulley system shown and released fromrest at initial time t0 at a distance H = 3 ft above the stopper asshown. The stopper has a hole in it which allows the narrower block3 to pass through. However, when block 2 contacts the stopper,block 2's motion stops, and only blocks 1 and 3 continue tomove.

a) What is the change in gravitational potential energy of thesystem from the initial time t0 to the time t1 immediately beforeblock 2 contacts the stopper?

HELP: Use kinematics to relate the positions and velocities of theblocks.

b)What is the kinetic energy of the system at time t1 immediatelybefore it contacts the stopper?

HELP: What is the initial kinetic energy of the system?
HELP: Conserve energy from time t0 to time t1 just before block 2contacts the stopper.

c)What is the speed of block 2 at time t1 immediately before itcontacts the stopper?

HELP: This problem involves translation only, so you may usekinetic energy T=(mv^2) /2 for each block.

d)What is the kinetic energy of the system at time t2 just afterblock 2 contacts the stopper, i.e. the system in which blocks 1 and3 continue their motion without block 2?

HELP: Is (mechanical) energy conserved during the collision betweenblock 2 and the stopper from time t1 to time t2?
HELP: No, it is not. Has the moving mass of the systemchanged?
HELP: Have the speeds of the blocks that continue to movechanged?

e)When block 3 first comes to rest at time t3 (after passingthrough the stopper), how far will it be from where itstarted?

HELP: Conserve energy from the time immediately after the collisionbetween block 2 and the stopper to the time when blocks 1 and 3stop, i.e. from time t2 to time t3.
HELP: Carefully consider for what the question is asking.

Question 1 of 7 0.5 Points
A 6 N force acts on a 0.3-kg object for 0.3 seconds. By how muchdoes the object's momentum change (in kg-m/s)?

Question 2 of 7 0.5 Points
A 0.4-kg object is traveling to the right (in the positivedirection) with a speed of 1 m/s. After a 0.2 s collision, theobject is traveling to the left at 3 m/s. What is the magnitude ofthe impulse (in N-s) acting on the object? The answer must bepositive.

Question 3 of 7 1.0 Points
The force shown in the attached figure is the net eastward forceacting on a ball. The force starts rising at t = 0.020 s, fallsback to zero at t = 0.062 s, and reaches a maximum force of 55 N atthe peak. Determine with an error no bigger than 25% (high or low)the magnitude of the impulse (in N-s) delivered to the ball. Hint:Do not use J = F?t. Look at the figure. Find the area of a nearlyequally sized triangle.

Question 4 of 7 1.0 Points
A bat hits a moving baseball. If the bat delivers a net eastwardimpulse of 0.6 N-s and the ball starts with an initial horizontalvelocity of 3.8 m/s to the west and leaves with a 5.2m/s velocityto the east, what is the mass of the ball (in grams)?
Part 5 of 7 -

Question 5 of 7 0.5 Points
The force sensor measures the force on the sensor due to thebumper, but the cart's momentum change arises from the force on thecart due to the bumper. Which of the following facts are needed toassert that the magnitude of these two forces are nearly equal atall times.
1. Their magnitudes differ by the magnitude of the net force on thebumper.
2. The force of friction is small.
3. The net force on the bumper is small.
4. The cart's weight is canceled by the the normal force exerted bythe track.

A. 1, 3

B. 2, 4

C. 3, 4

D. 1, 2

E. 1, 4

F. 1, 2, 3, 4

G. 2, 3

Part 6 of 7 -

Question 6 of 7 1.0 Points
A cart traveling at 0.3 m/s collides with stationary object. Afterthe collision, the cart rebounds in the opposite direction. Thesame cart again traveling at 0.3 m/s collides with a differentstationary object. This time the cart is at rest after thecollision. In which collision is the impulse on the cartgreater?

A. The second collision.

B. Cannot be determined without knowing the mass of the cart.

C. The impulses are the same.

D. The first collision.

E. Cannot be determined without knowing the rebound speed of thefirst collision. Reset Selection

Part 7 of 7 -

Question 7 of 7 0.5 Points
The force vs. time graphs for two collisions are shown. Whichcollision has the largest impulse?

A. The impulse for collision 2 since it lasts longer.

B. Cannot be determined since the masses are unknown.

C. The impulse for collision 1 since it has the larger maximumforce.

D. Cannot be determined since the initial an final speeds areunknown.

E. The impulses are the same.

PHY180H1 Midterm: PHY180H1_20179_621513059567TT2examsoln2017b

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