Answer:
t = 13.9s
Explanation:
u = 0 m/s
v = 75 km/h
= 20.83 m/s
a = 1.5 m/s²
Using
v = u + at
20.83 = 0 + 1.5t
t = 13.9s
A 230 kg steel crate is being pushed along a cement floor. The force of friction is 480 N to the left and the applied force is 1
1 answer:
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(a) 196 N
The equation of the forces on the side of the cord where the force F is applied is:
(1)
where T is the tension in the cord.
On the other side of the cord, the equation of the forces on the canister is
(2)
where
m = 20 kg is the mass of the canister
is the acceleration of gravity
a is the acceleration
From (1),
Substituting into (2),
We want the canister to move at constant speed, so
a = 0
And therefore:
b) 2.0 cm
The cord is inextensible, this means that the acceleration of its parts are the same. Therefore, the acceleration of the free end must be the same as the acceleration of the canister: and this means that the two parts also cover the same distance in the same time.
Therefore, the free end of the cord must be moved exactly the same as the canister, by 2.0 cm.
c) 3.92 J, the same
The work done by the tension in the cord is
where
T is the tension
d = 2.0 cm = 0.02 m is the displacement
As we said in part (a), the tension in the cord is equal to the force applied to the free end:
T = F
So
T = 196 N
Therefore, the work done by the tension is
And since the force applied (F) is the same, then the work done by you when pulling the cord is exactly the same.
(d) -3.92 J
The weight of the canister is
However, the direction of the force of gravity is opposite to the displacement. Therefore, the work done by gravity is negative:
And substituting,
(e) Zero
The net work done on the canister can be simply calculated by adding the work done by the tension in the cord and the weight of the canister:
This is in agreement with the work-energy theorem, which states that the work done on an object is equal to its change in kinetic energy. In this situation, the canister is moving at constant speed, so its kinetic energy is not change: therefore,
(change in kinetic energy = 0)
and so, the work done on it is also zero.
(f) The pulley system changes the direction of the force applied
This is a simple pulley system, which means that the system does not multiply the force applied in input. In fact, the mechanical advantage of the system is
where:
is the output force, which is the weight of the canister
is the force in input, which is F
So, the mechanical advantage is 1:
From a point of view of energy, therefore, there is no advantage in this system.
However, the advantage offered by the pulley system concerns the direction of the force: in fact, it changes the direction of the applied force (which is F, downward) into the tension of the cord (which is upward on the canister).
Answer:
Explanation:
mass of car, m = 1022 kg
mass of truck, M = 1620 kg
initial velocity of truck, U = 14.5 m/s
initial velocity of car, u = 0 m/s
Let the final velocity of car is v and the final velocity of truck is V.
Collision is elastic, so the coefficient of restitution, e = 1
Use conservation of momentum
initial momentum of car + initial momentum of truck = final momentum of car + final momentum of truck
m x u + M x U = m x v + M x V
0 + 1620 x 14.5 = 1022 v + 1620 V
23490 = 1022 v + 1620 V ..... (1)
Use the formula of coefficient of restitution
1 (14.5 - 0) = v - V
14.5 = v - V
V = v - 14.5 .... (2)
Put in equation (1)
23490 = 1022 v + 1620 (v - 14.5)
23490 = 1022 v + 1620 v - 23490
46980 = 2642 v
v = 17.8 m/s
Put in equation (2)
V = 17.8 - 14.5
V = 3.3 m/s
Thus, the speed of car is 17.8 m/s and the velocity of truck is 3.3 m/s after collision.
Refraction refers to C. the bending of light rays when they pass from one medium into another
Explanation:
Refraction is a phenomenon typical of wave. Refraction occurs when a wave travels through the boundary between two different mediums. When this occurs, the wave changes speed, wavelength and direction (but the frequency remains the same).
In particular, the direction of the refracted ray is determined by Snell's Law:
where
is the index of refraction of the 1st medium
is the index of refraction of the 2nd medium
is the angle of incidence, which is the angle between the direction of the incident wave and the normal to the boundary
is the angle of refraction, which is the angle between the direction of the refracted wave and the normal to the boundary
Therefore, the correct description of refraction is
C. the bending of light rays when they pass from one medium into another
Learn more about refraction:
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