PHYSICS 2305 test 3

Angie, Brad, and Carlos are discussing a physics problem in which two identical bullets are fired with equal speeds at equal-mass wood and steel blocks resting on a frictionless table. One bullet bounces off the steel block while the second becomes embedded in the wood block. Part A "All the masses and speeds are the same," says Angie, "so I think the blocks will have equal speeds after the collisions." "But what about momentum?" asks Brad. "The bullet hitting the wood block transfers all its momentum and energy to the block, so the wood block should end up going faster than the steel block." "I think the bounce is an important factor," replies Carlos. "The steel block will be faster because the bullet bounces off it and goes back the other direction." Which of these three do you agree with?

Carlos

A 1500 kg weather rocket accelerates upward at 10m/s2. It explodes 2.0 s after liftoff and breaks into two fragments, one twice as massive as the other. Photos reveal that the lighter fragment traveled straight up and reached a maximum height of 530 m. Part A What was the speed of the heavier fragment just after the explosion?

-20.0 m/s

A 63 kg student is standing atop a spring in an elevator that is accelerating upward at 2.9 m/s2 . The spring constant is 2200 N/m . Part A By how much is the spring compressed?

0.36 m

A stock person at the local grocery store has a job consisting of the following five segments: (1) picking up boxes of tomatoes from the stockroom floor (2) accelerating to a comfortable speed (3) carrying the boxes to the tomato display at constant speed (4) decelerating to a stop (5) lowering the boxes slowly to the floor. During which of the five segments of the job does the stock person do positive work on the boxes?

1 and 2

You've taken a summer job at a water park. In one stunt, a water skier is going to glide up the 2.0-m-high frictionless ramp shown in the figure, then sail over a 5.0-m-wide tank filled with hungry sharks. You will be driving the boat that pulls her to the ramp. She'll drop the tow rope at the base of the ramp just as you veer away. (Figure 1) Part A What minimum speed must you have as you reach the ramp in order for her to live to do this again tomorrow?

10.0 m/s

Truck brakes can fail if they get too hot. In some mountainous areas, ramps of loose gravel are constructed to stop runaway trucks that have lost their brakes. The combination of a slight upward slope and a large coefficient of rolling friction as the truck tires sink into the gravel brings the truck safely to a halt. Suppose a gravel ramp slopes upward at 6.0∘ and the coefficient of rolling friction is 0.43. Part A Use work and energy to find the length of a ramp that will stop a 15,000 kg truck that enters the ramp at 34 m/s .

110 m

The spring in the figure has a spring constant of 1300 N/m . It is compressed 17.0 cm , then launches a 200 g block. The horizontal surface is frictionless, but the block's coefficient of kinetic friction on the incline is 0.190. Height of ramp is 2 m (Figure 1) Part A What distance d does the block sail through the air?

14.4 m

Part C A sprong-loaded toy gun shoots a 19 g plastic ball. What is the launch speed if the sprong constant is 4.6×104 N/m3 and the sprong is compressed 13 cm ? Assume the barrel is frictionless.

19 m/s

The left end of a spring is attached to a wall. When Bob pulls on the right end with a 200 N force, he stretches the spring by 28 cm . The same spring is then used for a tug-of-war between Bob and Carlos. Each pulls on his end of the spring with a 200 N force. Part A How far does the spring stretch?

28 cm

Force Fx=(10N)sin(2πt/4.0s) (where t in s) is exerted on a 420 g particle during the interval 0s≤t≤2.0s. Part A If the particle starts from rest, what is its speed at t=2.0s?

30 m/s

A 16 kg child slides down a 2.6-m-high playground slide. She starts from rest, and her speed at the bottom is 2.0 m/s . Part A What is the change in the combined thermal energy of the slide and the seat of her pants?

380 J

A roller-coaster car rolls down a frictionless track, reaching speed v0 at the bottom. If you want the car to go twice as fast at the bottom, by what factor must you increase the height of the track?

4

The parking brake on a 2000 kg Cadillac has failed, and it is rolling slowly, at 4.00 mph , toward a group of small children. Seeing the situation, you realize you have just enough time to drive your 2000 kg Volkswagen head-on into the Cadillac and save the children. Part A With what speed should you impact the Cadillac to bring it to a halt

4 mph

It's been a great day of new, frictionless snow. Julie starts at the top of the 60∘ slope shown in the figure(Figure 1) . At the bottom, a circular arc carries her through a 90∘ turn, and she then launches off a 3.0-m-high ramp. Part A How far horizontally is her touchdown point from the end of the ramp?

43m

A student places her 430 g physics book on a frictionless table. She pushes the book against a spring, compressing the spring by 7.90 cm , then releases the book. Part A What is the book's speed as it slides away? The spring constant is 1750 N/m .

5.04 m/s

A 36.0 g ball is fired horizontally with initial speed v0 toward a 110 g ball that is hanging motionless from a 1.10 m -long string. The balls undergo a head-on, perfectly elastic collision, after which the 110 g ball swings out to a maximum angle θmax = 51.0 ∘. Part A What was v0?

5.73 m/s

A 1500 kg car traveling at 12 m/s suddenly runs out of gas while approaching the valley shown in the figure(Figure 1) . The alert driver immediately puts the car in neutral so that it will roll. Part A What will be the car's speed as it coasts into the gas station on the other side of the valley?

6.8 m/s

A cannon tilted up at a 25.0 ∘ angle fires a cannon ball at 65.0 m/s from atop a 30.0 m -high fortress wall. Part A What is the ball's impact speed on the ground below?

69.4 m/s

A freight company uses a compressed spring to shoot 1.60 kg packages up a 1.00-m -high frictionless ramp into a truck, as the figure(Figure 1) shows. The spring constant is 265 N/m and the spring is compressed 35.0 cm . Part A What is the speed of the package when it reaches the truck? Part B A careless worker spills his soda on the ramp. This creates a 50.0-cm-long sticky spot with a coefficient of kinetic friction 0.300. Will the next package make it into the truck?

A: 0.828 m/s B: No (should get a negative distance)

One billiard ball is shot east at 1.9 m/s . A second, identical billiard ball is shot west at 0.80 m/s . The balls have a glancing collision, not a head-on collision, deflecting the second ball by 90∘ and sending it north at 1.38 m/s . Part A What is the speed of the first ball after the collision? Part B What is the direction of the first ball after the collision? Give the direction as an angle south of east.

A: 1.8 m/s B: 51 degrees

Part A How much work is done by the force F⃗ =(− 3.5 i^− 5.2 j^)N on a particle that moves through displacement Δr⃗ = − 2.9 i^m Part B How much work is done by the force F⃗ =(− 3.5 i^− 5.2 j^)N on a particle that moves through displacement Δr⃗ = 2.9 i^−2.0j^m?

A: 10 J B: 0.25 J

A 65 kg sprinter, starting from rest, runs 40 m in 7.0 s at constant acceleration. Part A What is the magnitude of the horizontal force acting on the sprinter? Part B What is the sprinter's power output at 2.0 s, 4.0 s, and 6.0 s?

A: 110 N B: 0.35,0.69,1.0 kW

A firecracker in a coconut blows the coconut into three pieces. Two pieces of equal mass fly off south and west, perpendicular to each other, at 20 m/s. The third piece has twice the mass as the other two. Part A What is the speed of the third piece? Part B What is the direction of the third piece? Give the direction as an angle east of north.

A: 13 m/s B: 45 degrees east of north

A 49.0 kg ice skater is gliding along the ice, heading due north at 4.10 m/s . The ice has a small coefficient of static friction, to prevent the skater from slipping sideways, but μk =0. Suddenly, a wind from the northeast exerts a force of 3.70 N on the skater. Part A Use work and energy to find the skater's speed after gliding 100 m in this wind. Part B What is the minimum value of μs that allows her to continue moving straight north?

A: 2.48 m/s B: 5.45*10^-3

A package of mass m is released from rest at a warehouse loading dock and slides down the h = 3.0 m - high, frictionless chute to a waiting truck. Unfortunately, the truck driver went on a break without having removed the previous package, of mass 2m, from the bottom of the chute. (Figure 1) Part A Suppose the packages stick together. What is their common speed after the collision?

A: 2.6 m/s B: 33 cm/s

Most geologists believe that the dinosaurs became extinct 65 million years ago when a large comet or asteroid struck the earth, throwing up so much dust that the sun was blocked out for a period of many months. Suppose an asteroid with a diameter of 2.0 km and a mass of 9.0×1012 kg hits the earth with an impact speed of 4.5×104 m/s . Part A What is the earth's recoil speed after such a collision? (Use a reference frame in which the earth was initially at rest.) Use the astronomical data inside the back cover of the textbook. Part B What percentage is this of the earth's speed around the sun?

A: 6.8*10^-8 m/s B: 2.3 *10^-10 %

Two ice skaters, Paula and Ricardo, push off from each other. Ricardo weighs more than Paula. Part A Which skater, if either, has the greater momentum after the push-off? Which skater, if either, has the greater speed after the push-off?

A: Both have the same momentum B: Paula

A clever engineer designs a "sprong" that obeys the force law Fx=−q(x−xe)3, where xe is the equilibrium position of the end of the sprong and q is the sprong constant. For simplicity, we'll let xe=0m. Then Fx=−qx3. Part A What are the units of q? Part B Find an expression for the potential energy of a stretched or compressed sprong.

A: N/m^3 B: 1/4qx^4 C:

Two balls of clay of known masses hang from the ceiling on massless strings of equal length. They barely touch when both hang at rest. One ball is pulled back until its string is at 45 ∘ , then released. It swings down, collides with the second ball, and they stick together. Part A To determine the angle to which the balls swing on the opposite side, would you invoke: conservation of momentum, conservation of mechanical energy, both, either but not both, or these principles alone are not sufficient to find the angle?

Both

A small car has a head-on collision with a large truck. Which of the following statements concerning the magnitude of the average force due to the collision is correct?

Both experience the same average force

A 4.0-kg object is moving with speed 2.0 m/s. A 1.0-kg object is moving with speed 4.0 m/s. Both objects encounter the same constant braking force, and are brought to rest. Which object travels the greater distance before stopping?

Both travel the same distance

You drop a ball from a high balcony and it falls freely. Part A Does the ball's kinetic energy increase by equal amounts in equal time intervals, or by equal amounts in equal distances?

Equal amounts in equal distances

As a tile falls from the roof of a building to the ground its momentum is conserved. T or F

F

Jacques and George meet in the middle of a lake while paddling in their canoes. They come to a complete stop and talk for a while. When they are ready to leave, Jacques pushes George's canoe with a force F⃗ to separate the two canoes. What is correct to say about the final momentum and kinetic energy of the system(consisting of the two canoes and the men in them) if we can neglect any resistance due to the water?

Final momentum is zero but kinetic energy is positive

Two men, Joel and Jerry, push against a wall. Jerry stops after 10 min, while Joel is able to push for 5.0 min longer. Compare the work they do.

Neither does any work - no distance covered

A small glider is coasting horizontally when suddenly a very heavy piece of cargo falls out of the bottom of the plane. You can neglect air resistance. Just after the cargo has fallen out

Neither the cargo nor the plane change speed

If the force on a particle at some point in space is zero, must its potential energy also be zero at that point?

No

If the potential energy of a particle at some point in space is zero, must the force on it also be zero at that point?

No

A block of mass m slides down a frictionless track, then around the inside of a circular loop-the-loop of radius R. Part A From what minimum height h must the block start to make it around the loop without falling off? Give your answer as a multiple of R.

h/R=2.5

A 0.2 kg plastic cart and a 20 kg lead cart can both roll without friction on a horizontal surface. Equal forces are used to push both carts forward for a distance of 1 m, starting from rest. Part A After traveling 1 m, is the momentum of the plastic cart greater than, less than, or equal to the momentum of the lead cart?

less

On a smooth horizontal floor, an object slides into a spring which is attached to another mass that is initially stationary. When the spring is most compressed, both objects are moving at the same speed. Ignoring friction, what is conserved during this interaction?

momentum and mechanical energy

A baseball is thrown vertically upward and feels no air resistance. As it is rising

momentum is not conserved but mechanical energy is conserved

A process occurs in which a system's potential energy increases while the environment does work on the system. Part A Does the system's kinetic energy increase, decrease, or stay the same? Or is there not enough information to tell?

not enough info

A mother has four times the mass of her young son. Both are running with the same kinetic energy. Part A What is the ratio vs/vm other of their speeds?

vs/vm=2.0

If a force always acts perpendicular to an object's direction of motion, that force cannot change the object's kinetic energy. T or F

T

A 0.2 kg plastic cart and a 20 kg lead cart can both roll without friction on a horizontal surface. Equal forces are used to push both carts forward for a time of 1 s, starting from rest. Part A After the force is removed at t=1s, is the momentum of the plastic cart greater than, less than, or equal to the momentum of the lead cart?

equal