(a) What is the velocity of the cart after the collision?
(b) If the collision lasts 0.020 s, find the average force on the cart.
(c) Find the average force on the block.
| 1. A one dimensional collision occurs between a cart
of mass 11.0 kg moving to the right at 3.0 m/s and a block of mass 5.0 kg
moving to the left at 12.0 m/s. After the collision, the block moves to
the right at 4.0 m/s. (a) What is the velocity of the cart after the collision? (b) If the collision lasts 0.020 s, find the average force on the cart. (c) Find the average force on the block. |
|
| 2. A board is standing on the floor, and two different experiments are done. In one a piece of clay is thrown toward the top of the board, it collides and sticks to the board. In the other experiment, a superball is thrown that bounces off the top of the board. The masses of the board, the clay and the ball are the same, and the initial velocities are the same. In one experiment the board falls over, and in the other it wobbles but stays standing. Which object, clay or ball, made the board fall over? Explain. |  |
| 3. Two pucks move on a horizontal air-hockey table.
One puck has mass 3.0 kg and initially moves east at 4.0 m/s. The other
puck has a mass of 6.0 kg and moves at 5.0 m/s at 60° north of east,
as shown. The two pucks collide and stick together. (a) Find the velocity after the collision of the combined pucks. (b) If the collision lasts 35 ms, find the average force on the 3.0 kg puck. |
 |
4. The same two pucks as in problem 3 now collide and separate.
After the collision the 3.0 kg puck moves north at 1.0 m/s.
(a) Find the velocity of the 6.0 kg puck after the collision.
(b) If the collision lasts 35 ms, find the average force on the 3.0 kg puck.
|
5. A ball with mass 2.5 kg is moving in outer space with a velocity of 6.0 m/s horizontally, and a box of mass 4.5 kg is moving with a velocity of 4.0 m/s at an angle of 120° from the horizontal. The two collide and stick together. Find the final velocity of the pair. |
 |
| 6. Consider a rail car of mass 500 kg coasting along
a horizontal frictionless track at 3.0 m/s. I drop a 100 kg box from a height
of 60 cm into the car. (a) Find the final velocity of the car+box. (b) If the collision between the box and the car lasts 12 ms, find the average normal force that acts on the box during the collision. |
 |
George Benedik and Felix Villars, in Physics With Illustrative Examples From
Medicine And Biology, Volume 1, Addison Wesley, 1973, report that the threshold
for human survival is when the pressure on impact is less than 50 pounds/square
inch. If the fall is onto a person's back of area 3.8 square feet, the threshold
force for death is 27,000 pounds = 1.2 x 105 N.
In a fall from high altitude, the change in momentum is fixed by the terminal
velocity before impact, about 120 mph, and the velocity of 0 after what we hope
is not "Terminal" impact.
For the situations described below, find the average force and decide if the
situations satisfy this criterion for survival?
A. "During one of the battalion drops, from 1200 feet on a clear,
relatively warm day, an observer noted what appeared to be an unsupported bundle
falling from one of the C-119 airplanes; no chute deployed from the object.
The impact looked like a mortar round exploding in the snow. When the aidmen
reached the spot they found a young ... paratrooper flat on his back at the
bottom of a 3 1/2 foot crater in the snow, which consisted of alternating layers
of soft snow and frozen crust. He could talk and did not appear injured; nevertheless,
he was air evacuated to a hospital. His only injuries were an incomplete fracture
of a clavicle, a chip fracture of L-2, and a few bruises. He was released from
the hospital in time to return south with his unit."
Alaska, 1955
B. "[O]n the frigid 23rd of March, 1944, … Flight Sergeant Nicholas Alkemade, an RAF rear gunner [had his bomber set afire] by a German night fighter on a raid over Hamburg. [H]e found that he was unable to reach his parachute, stowed forward in the flaming fuselage. Deciding he didn't care to burn alive, he jumped without a parachute just as the aircraft exploded above him. His altitude was 18, 000 feet. Falling at a terminal velocity of about 120 mph during this 3 1/2 mile fall (which lasted about 90 seconds), he struck the snowy branches of a pine forest and then landed in less than 18 inches of snow, only twenty yards from the bare open ground. Incredibly, his only reported injuries consisted of superficial scratches and bruises, and burns received prior to the jump."
From "Terminal Velocity Impacts Into Snow", R. G. Snyder. Military
Medicine 131, 1290-1298 (1966).
This page maintained by Anne G. Young. Last modified 11-Oct-2004 .