Chapter 6 Conceptual Questions

A 35-N bucket of water is lifted vertically 3.0 m and then returned to its original position. How much work did gravity do on the bucket during this process?

0 J

How does the work required to stretch a spring 2 cm compare with the work required to stretch it 1 cm?

4 times the work

A cart starting from rest rolls down a hill and at the bottom has a speed of 4 m/s. If the cart were given an initial push, so its initial speed at the top of the hill was 3 m/s, what would be its speed at the bottom?

5 m/s

If a car traveling 60 km/hr can brake to a stop within 20 m, what is its stopping distance if it is traveling 120 km/hr? Assume that the braking force is the same in both cases.

80 m

A 1-kg ball is released from a height of 6 m, and a 2-kg ball is released from a height of 3 m. Air resistance is negligible as they fall.

As they reach the ground: both balls will have the same kinetic energy, and the 1-kg ball will be moving faster than the 2-kg ball.

Two identical grasshoppers jump into the air with the same initial speed and experience no air resistance. Grasshopper A goes straight up, but grasshopper B goes up at a 66° angle above the horizontal.

At their highest point: grasshopper A has more GPE than grasshopper B, both of them have the same ME, and grasshopper B is moving faster than grasshopper A.

A heavy frog and a light frog jump straight up into the air. They push off in such away that they both have the same kinetic energy just as they leave the ground. Air resistance is negligible.

Both frogs reach the same maximum height, and just as they leave the ground the lighter frog is moving faster than the heavier frog

Three cars (car L, car M, and car N) are moving with the same speed and slam on their brakes. The most massive car is car L, and the least massive is car N. If the tires of all three cars have identical coefficients of kinetic friction with the road surface, for which car is the amount of work done by friction in stopping it the greatest?

Car L

You slam on the brakes of your car in a panic, and skid a certain distance on a straight level road. If you had been traveling twice as fast, what distance would the car have skidded, under the same conditions?

It would have skidded 4 times farther

A truck has four times the mass of a car and is moving with twice the speed of the car. If Kt and Kc refer to the kinetic energies of truck and car respectively, it is correct to say that

Kt= 16Kc

You see a leaf falling to the ground with constant speed. When you first notice it, the leaf has initial total energy PEi + KEi. You watch the leaf until just before it hits the ground, at which point it has final total energy PEf + KEf. How do these total energies compare?

PEi + KEi > PEf + KEf

A mass attached to a vertical spring causes the spring to stretch and the mass to move downwards. What can you say about the spring's potential energy (PEs) and the gravitational potential energy (PEg) of the mass?

PEs increases and PEg decreases

A heavy dart and a light dart are launched horizontally on a frictionless table by identical ideal springs. Both springs were initially compressed by the same amount.

The darts both have the same kinetic energy just as they move free of the spring, the lighter dart leaves the spring moving faster than the heavy dart, and both darts had the same initial elastic potential energy.

A heavy sled and a light sled, both moving horizontally with the same speed, suddenly slide onto a rough patch of snow and eventually come to a stop. The coefficient of kinetic friction between the sleds and the rough snow is the same for both of them.

The friction from the snow will do more negative work on the heavy sled than on the light sled, and both sleds will slide the same distance on the rough snow before stopping

A heavy sled and a light sled, both moving horizontally with the same kinetic energy, suddenly slide onto a rough patch of snow and eventually come to a stop. The coefficient of kinetic friction between the sleds and the rough snow is the same for both of them.

The friction from the snow will do the same amount of work on both sleds, the light sled will slide farther than the heavy sled, and the change in KE will be the same for both sleds

A heavy stone and a light stone are released from rest in such away that they both have the same amount of gravitational potential energy just as they are released. Air resistance is negligibly small.

The stones both have the same kinetic energy just as they reach the ground, the light stones is traveling faster than the heavy stone just as it reaches the ground, and the initial height of the light stone is greater than the initial height of the heavy stone

You throw a baseball straight up. Compare the sign of the work done by gravity while the ball goes up with the sign of the work done by gravity while it goes down.

The work is negative on the way up and positive on the way down.

Three cars (car F, car G, and car H) are moving with the same speed and slam on their brakes. The most massive car is car F, and the least massive is car H. If the tires of all three cars have identical coefficients of kinetic friction with the road surface, which car travels the longest distance to skid to a stop?

They all have the same distance in stopping

A lightweight object and a very heavy object are sliding with equal speeds along a level frictionless surface. They both slide up the same frictionless hill with no air resistance. Which object rises to a greater height?

They both slide to exactly the same height

A heavy rock and a light rock are dropped from the same height and experience no significant air resistance as they fall.

When they reach the ground: the heavier rock has more kinetic energy than the lighter rock, and they both have the same speed

In a baseball game, the catcher stops a 90-mph pitch. What can you say about the work done by the catcher on the ball?

catcher has done negative work

When you pay the electric company by the kilowatt-hour, what are you actually paying for?

energy

A box is being pulled across a rough floor at a constant speed. What can you say about the work done by friction?

friction does negative work

A box sliding on a frictionless flat surface runs into a fixed spring, which compresses a distance x to stop the box. If the initial speed of the box were doubled, how much would the spring compress in this case?

twice as much

Two stones, one twice the mass of the other, are dropped from a cliff. Just before hitting the ground, what is the kinetic energy of the heavy stone compared to the light one?

twice as much