Relative Motion 1D
Two cars are moving in the same direction on a straight road. Car A moves at 30 km/h and Car B moves at 50 km/h. What is the velocity of Car B relative to Car A?
vBA=20 km/h
In the example of a boat that crosses a flowing river. Which of the following is the correct triangle of vector (and displacement) velocities:
Acute triangle – all angles are less than 90°.
Right triangle – one angle is exactly 90°.
Obtuse triangle – one angle is greater than 90°.
Right triangle
True or False: In a Uniform Circular Motion the speed is constant
True
True or False: The centripetal acceleration is parallel to the tangent velocity
False (It is perpendicular as it points to the centre of the circular path)
A train is moving at 60 km/h and a person walks inside the train at 5 km/h in the same direction as the train. What is the speed of the person relative to the ground?
v (person/ground) = 65 km/h
The velocity and displacement triangles in a relative motion graphic have:
- same angles and side lengths
- same angles but not same side lengths
- same side lengths but not same angles
Same angles but not same side lengths (similar triangles)
True or False: In a Uniform Circular Motion the velocity is constant
False
Why an object in Uniform circular motion has an acceleration? (centripetal acceleration)
Because the speed is constant, but the velocity change, owing to the change in diretion of the velocity vector along the circular path.
Two cyclists are moving towards each other. Cyclist A moves at 12 m/s and Cyclist B moves at 8 m/s. What is the velocity of Cyclist B relative to Cyclist A?
vBA = 20 m/s
A boat can move at 12 m/s in still water. It crosses a river flowing at 6 m/s (drift velocity) perpendicular to the boat’s path. Find the velocity of the boat relative to the riverbank (ground).
v(boat/ground) = 13.42 m/s
Where does the centripetal acceleration points?
To the centre of the circular path
An object travels with a tangent velociy of 12 m/s through in a circular path having a radius of 27 m, find the angular speed (in rad/s).
0.444 rad/s
Two cars move on parallel roads in opposite directions. Car A moves at 40 m/s and Car B moves at 60 m/s (both with reference to a static observer O). If the cars are initially 500 m apart, how long does it take for them to meet?
t = 5 s
A boat can move at 10 m/s in still water. It crosses a river flowing at 4 m/s (drift velocity) perpendicular to the boat’s path. Knowing the velocity(boat/ground)=10.77 m/s, and the river width is 100 m, find the time to reach the other side.
t=10 s
An object in circular motion travels with centripetal acceleration of 6 m/s^2. If the radius of the circular path is 18 m, find the magnitude of the tangent velocity.
10.4 m/s (approximately)
A satellite is orbiting Earth in a circular path of radius 7.0×10^6 m. Its tangential speed is 7.5×10^3 m/s.
Find the period of the satellite in second (the time it takes to complete one full revolution around Earth).
T=5864 s