Complete the first and second sentences, choosing the correct answer from the given ones.
1 answer:
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Answer:
His kinetic energy increases, potential energy decreases
The sum of kinetic and potential energy is a constant at any instant before he comes to rest.
Explanation:
Snowboarder is starting from a height and moving to the down direction. As he moves down his velocity increases, we know that kinetic energy is given by the expression , so as he moves his kinetic energy increases.
When the snowboarder is starting his potential energy is maximum(Potential energy = mgh), as he comes down his potential energy decreases.
Based on this we can conclude that the sum of potential energy and kinetic energy is a constant at any instant for a snowboarder before he comes to rest.
mgh+= Constant
The text does not specify whether the resistance R of the wire must be kept the same or not: here I assume R must be kept the same.
The relationship between the resistance and the resistivity of a wire is
where
is the resistivity
A is the cross-sectional area
R is the resistance
L is the wire length
the cross-sectional area is given by
where r is the radius of the wire. Substituting in the previous equation ,we find
For the new wire, the length L is kept the same (L'=L) while the radius is doubled (r'=2r), so the new resistivity is
Therefore, the new resistivity must be 4 times the original one.
The relationship between the resistance and the resistivity of a wire is
where
A is the cross-sectional area
R is the resistance
L is the wire length
the cross-sectional area is given by
where r is the radius of the wire. Substituting in the previous equation ,we find
For the new wire, the length L is kept the same (L'=L) while the radius is doubled (r'=2r), so the new resistivity is
Therefore, the new resistivity must be 4 times the original one.
Hello!
A 10-kg cart moving at 5 m/s collides with a 5-kg cart at rest and causes it to move 10 m/s. Which principle explains the result? A) law of differential mass B) law of conservation of momentum C) law of unequal forces D) law of accelerated collision
We have the following data¹:
ΔP (momentum before impact) = ?
mA (mass) = 10 kg
vA (velocity) = 5 m/s
mB (mass) = 5 kg
vB (velocity) = 0 m/s
Solving:
ΔP = mA*vA + mB*vB
ΔP = 10 kg*5 m/s + 5 kg*0 m/s
ΔP = 50 kg*m/s + 0 kg*m/s
Δp = 50 kg*m/s ← (momentum before impact)
We have the following data²:
ΔP (momentum after impact) = ?
mA (mass) = 10 kg
vA (velocity) = 0 m/s
mB (mass) = 5 kg
vB (velocity) = 10 m/s
Solving:
Δp = mA*vA + mB*vB
Δp = 10 kg*0 m/s + 5 kg*10 m/s
Δp = 0 kg*m/s + 50 kg*m/s
Δp = 50 kg*m/s ← (momentum after impact)
*** Then, which principle explains the result ?
Law of conservation of momentum, <u>since the total momentum of body A and B before impact is equal to the total momentum of body A and B after impact.</u>
Note: Bodies of different masses and velocities may have the same kinetic energy, if proportionality between the units is maintained it can occur that they have the same kinetic energy.
Answer:
B) law of conservation of momentum
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