Answer:
If the person is to remain the floor the reaction force will be equal to the normal force exerted by the floor.
F(normal) - F(reaction) = 0
That means the person is not moving with respect to the elevator.
Expanding the applied forces we have:
Fw - Fn = 720 - 710 = 10 N where the positive direction is chosen as down
Fw is the weight of the person and Fn the force exerted on the person by the elevator,
The acceleration of the person the becomes F = m a = m * 10 N and will be downward agreeing with our choice of coordinate axes.
1. lifts it chest high
The force opposing to this action is the force due to
gravity. Therefore the work done is:
W1 = m g d
where m is mass of the barbell, g is gravity and d is displacement
2. holds it for 30 seconds
Work is a product of force and displacement, since there
is no displacement, therefore work done is zero.
W2 = 0
3. puts it down slowly
If the barbell was dropped, then it would simply be a free
fall. But since it was not, so the work done here is also equal to the weight
of the barbell times displacement:
W3 = m g d
We can see that W1 = W3, and since W2 = 0, therefore the answer
is:
<span>w3 = w1 > w2</span>
Answer:
1 second
Explanation:
The impulse exerted on the boy is equal to its change of momentum:
where
F = 500 N is the push on the boy
is the contact time
m = 25 kg is the mass of the boy
is the change in velocity of the boy
Solving the formula for the contact time, we find
The first law of thermodynamics can be written as
where
is the variation of internal energy of the system
is the amount of heat absorbed by the system
is the work done by the system on the surrounding.
Using this form, the sign convention for Q and W becomes:
Q > 0 --> heat absorbed by the system (because it increases the internal energy)
Q < 0 --> heat released by the system (because it decreases the internal energy)
W > 0 --> work done by the system (for instance, an expansion: when the system expands, it does work on the surrounding, and so the internal energy decreases, this is why there is a negative sign in the formula Q-W)
W < 0 --> work done by the surrounding on the system (for instance, a compression: when the system is compressed, the surrounding is doing work on the system, and so the internal energy of the system increases)
velocity = traveled distance ÷ time of the traveled distance is seconds
velocity = 600 ÷ 60
velocity = 10 m/s
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Kinetic Energy = 1/2 × mass × ( velocity )^2
KE = 1/2 × 60 × ( 10 )^2
KE = 30 × 100
KE = 3000 j