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Question
White-light LEDs employA) phosphors.
B) white-emitting diodes.
C) extra-high electrical barriers.
D) none of the above
Answer
This answer is hidden. It contains 1 characters.
Related questions
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If the speed of a bicycle is reduced to half before skidding to a stop, it will skid
A) one-eighth as far.
B) one-fourth as far.
C) one-half as far.
D) none of the above
Q:
A cannonball has more kinetic energy than the recoiling cannon from which it is fired because the force on the ball
A) is more concentrated.
B) meets less resistance than the cannon on the ground.
C) acts over a longer distance.
Q:
If a Ping-Pong ball and a golf ball both move in the same direction with the same amount of kinetic energy, the speed of the Ping-Pong ball must be
A) less than the golf ball.
B) more than the golf ball.
C) both the same
D) need more information
Q:
A cannonball following a parabolic path explodes into fragments. The momentum of the fragments
A) continue along the path as if the explosion didn't occur.
B) cancels to zero by vector addition.
C) both of these
D) neither of these
Q:
A golf ball moving forward with 1 unit of momentum strikes and bounces backward off a heavy bowling ball that is initially at rest and free to move. The bowling ball is set in motion with a momentum of
A) less than 1 unit.
B) more than 1 unit.
C) 1 unit.
D) not enough information
Q:
A fan attached to an ice sailcraft stalled on a windless day blows air into the sail that bounces backward upon impact. The boat
A) moves in the direction of the wind impact force.
B) does not move by this wind impact.
C) moves, but in the opposite direction of the wind impact force.
Q:
If a monkey floating in outer space throws his hat away, the hat and the monkey will both
A) move away from each other, but at different speeds.
B) move away from each other at the same speed.
C) move a short distance and then slow down.
D) move a short distance and then go faster.
E) come to a stop after a few minutes.
Q:
Two billiard balls having the same mass and speed roll toward each other. What is their combined momentum after they meet?
A) zero
B) half the sum of their original momentums
C) twice the sum of their original momentums
D) need more information
Q:
Recoil is noticeable if we throw a heavy ball while standing on roller skates. If instead we go through the motions of throwing the ball but hold onto it, our net recoil will be
A) zero.
B) the same as before.
C) small, but noticeable.
Q:
The average braking force of a 1000-kg car moving at 10 m/s braking to a stop in 5 s is
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B) 2000 N.
C) 3000 N.
D) 4000 N.
E) 5000 N.
Q:
When you jump from an elevated position you usually bend your knees upon reaching the ground, which makes the time of the contact about 10 times that of a stiff-legged landing. In this way the average force your body experiences is
A) less than 1/10 as great.
B) more than 1/10 as great.
C) about 1/10 as great.
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Q:
Padded dashboards in cars are safer in an accident than non-padded ones because passengers hitting the dashboard encounter
A) lengthened time of contact.
B) shorter time of contact.
C) decreased impulse.
D) increased momentum.
Q:
It is correct to say that impulse is equal to
A) momentum.
B) a corresponding change in momentum.
C) force multiplied by the distance it acts.
D) velocity multiplied by time.
Q:
A motorcycle of mass 100 kilograms slowly rolls off the edge of a cliff and falls for three seconds before reaching the bottom of a gully. Its momentum upon hitting the ground is
A) 1,000 kg m/s.
B) 2,000 kg m/s.
C) 3,000 kg m/s.
D) 4,000 kg m/s.
E) 9,000 kg m/.
Q:
The mass of a ball moving at 3 m/s with a momentum of 48 kg m/s is
A) 4 kg.
B) 12 kg.
C) 16 kg.
D) 144 kg.
E) none of these
Q:
The speed of a 4-kg ball with a momentum of 12 kg m/s is
A) 3 m/s.
B) 4 m/s.
C) 12 m/s.
D) 48 m/s.
E) none of the above
Q:
A freight train rolls along a track with considerable momentum. If it rolls at the same speed but has twice as much mass, its momentum is
A) zero.
B) twice.
C) four times as much.
D) unchanged.
Q:
A river 100 m wide flows due south at 1 m/s. A boat that goes 1 m/s relative to the water leaves the west bank. To land at a point due east of its starting point, the boat must be pointed
A) northeast.
B) east.
C) southeast.
D) nowhere"it can't be done.
Q:
A pair of equal-length vectors at right angles to each other have a resultant. If the angle between the vectors is greater than 90o, their resultant is
A) less.
B) the same.
C) greater.
Q:
When Monkey Mo is suspended at rest by holding a rope with one hand and the side of his cage with the other, all the force vectors that act on him
A) have equal magnitudes.
B) cancel except for his weight vector, mg.
C) have a vector sum of zero.
Q:
As the sloped surface supporting a shoe becomes steeper
A) the shoe's weight mg remains unchanged.
B) the normal force becomes less.
C) friction needed to keep it at rest increases.
D) all of the above
E) none of the above
Q:
The force due to gravity that acts on a block of ice that slides down an icy ramp
A) remains equal to mg at all angles.
B) decreases as the slope of the ramp increases.
C) becomes greatest when the ramp is vertical.
Q:
When Nellie hangs suspended from a pair of ropes that are not vertical, the tension in each rope is
A) less than half her weight.
B) half her weight.
C) more than half her weight.
D) her weight.
Q:
When a cannonball is fired from a cannon, which undergoes the greater acceleration?
A) the cannonball
B) the recoiling cannon
C) both the same
Q:
A pair of toy freight cars, one twice the mass of the other, fly apart when a compressed spring that joins them is released. Acceleration will be greater for the
A) heavier car.
B) lighter car.
C) same on each.
Q:
The force with which Earth pulls on the Moon is
A) somewhat greater than Moon's pull on Earth.
B) the only force acting between Earth and Moon.
C) equal in magnitude to the force that Moon pulls on Earth.
Q:
As a ball falls, the action force is the Earth's pull on the ball. The reaction force is the
A) air resistance acting against the ball.
B) acceleration of the ball.
C) ball's pull on Earth.
D) none of the above
Q:
To produce an acceleration to a system there
A) must be a net force on the system.
B) may or may not be a net force on the system.
C) must be acceleration outside the system also.
Q:
An archer shoots an arrow. Consider the action force to be the bowstring against the arrow. The reaction to this force is the
A) combined weight of the arrow and bowstring.
B) friction of the ground against the archer's feet.
C) grip of the archer's hand on the bow.
D) arrow's push against the bowstring.
Q:
A fast-moving missile soaring overhead possesses
A) speed.
B) force.
C) both of these
D) neither of these