A subway train starts from rest at a station and accelerates uniformly at 1.8m/s^2 for 15 sec. then it runs at a constant speed for the next 35 sec. before decelerating at 2.0m/s^2 until it comes to rest at the next station. FIND THE DISTANCE between the stations and the AVERAGE SPEED of the train.(please show step by step and the formula that is used. Thank you!)
Answers
Take them one at a time:
First piece:
From rest, accelerates 1.8 m/s² for 15 sec.
Speed at the end of the 15 sec = 1.8 x 15 = 27 m/s
Distance covered = (average speed) x (time) = (13.5) x (15) = 202.5 meters
Middle piece:
Starts this piece at 27 m/s.
Runs at constant speed for 35 sec.
Covers (27 x 35) = 945 meters
Finishes this piece (15 + 35) = 50 seconds after leaving the first station
Finishes this piece (202.5 + 945) = 1147.5 meters from the first station.
Last piece:
Starts this piece 50 seconds after leaving the first station,
1147.5 meters from it, still moving at 27 m/s.
Decelerates at 2.0 m/s² .
--> It takes 27/2.0 = 13.5 seconds to come to a stop.
--> Distance covered during this piece = (average speed) x (time)
= (13.5 m/s) x (13.5 sec) = 182.25 meters
Finishes this piece (50 + 13.5) = 63.5 seconds after leaving the first station
Finishes this piece (1147.5 + 182.25) = 1,329.75 m from the first station
Distance between the stations (along the track) = 1,329.75 meters.
Average speed = (total distance) / (total time) = 1,329.75 / 63.5 = 20.941 m/s.
I sure hope I didn't make any stupid arithmetic blunders here,
because I really don't feel like going back and checking it.
Let me know, and I'll fix them.
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Answer:
u = 6.667 cm
Explanation:
given,
Focal length of the concave mirror, f = 20 cm
magnification factor = 1.5
we know,
v is the distance of the image
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Answer:
omg i uses to know this answer
Explanation:
but I forgot
Answers
Force is needed to change the speed or direction of an object moving at a constant speed.
We have an object is moving at a constant speed in one direction.
We have to determine what is needed to change its speed or direction.
Is Speed scalar or vector quantity ?
Speed is a scalar quantity as it has only magnitude and no direction.
According to the question, we have -
An object is moving at a constant speed in one direction. Now in order to change its speed or direction we need something to change its current state in which it is moving with constant speed in one direction. According to Newton's first law of motion, any body continues to be in its current state, unless some external force is applied on it. Hence, a certain amount of Force is needed in order to change its speed or direction.
Hence, Force is needed to change the speed or direction of an object moving at a constant speed.
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Any considerable amount of force is needed to change the speed of an object, if it is moving with constant speed in one direction. If the force applied is in the same direction in which an object is moving, speed of the object will increase. If force is in opposite direction of the motion, speed of object will decrease. If force is always perpendicular to the direction of motion of an object, it will move in a circle.
Further explanation:
Newton’s first law states that an object will remain in its initial state of the motion until and unless an external force is applied on the object. It means, object will remain in motion if it was in motion and it will remain at rest if it was initially at rest until and unless an external force is applied on the object.
Given:
An object is moving at a constant speed in one direction.
Concept:
Acceleration is defined as the rate of change of velocity with respect to time. Acceleration will be zero if change in the velocity with time is zero.
We know that velocity is a vector quantity because it has magnitude as well as the direction.
In the question object is moving in one direction, therefore direction is not changing with time, and also the magnitude of the velocity of an object is constant. So the acceleration of the object is zero.
Acceleration is caused due to the force. If all the forces on the object are in equilibrium, the net force on the object will be zero and acceleration of object will also be zero.
Now if we want to change the speed or direction of the object, it is needed to exert an external force on the object. If a net force is exerted on the object, it will be subjected to an acceleration which causes change in speed or change of direction of the object.
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Answer Details:
Grade: High School
Subject: Physics
Chapter: Laws of motion
Keywords:
Object, moving, constant, speed, one, direction, needed, change, speed, direction, considerable, force, acceleration, zero acceleration.
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