Question

Velocity from Force Diagram Ranking Task

Below are birds-eye views of six identical toy cars moving to the right at 2 m/s. Various forces act on the cars with magnitudes and directions indicated below. All forces act in the horizontal plane and are either parallel or at 45 or 90 degrees to the car's motion.

Part A

Rank these cars on the basis of their speed a short time (ie. before any car's speed can reach zero) after the forces are applied.

Rank from largest to smallest. To rank items as equivalent, overlap them.

Answer 1

In case A

force in +x-direction

Fx+ = 5 N

force in -x direction = 5*cos 45 deg + 5*cos 45 deg

Fx- = 7.07 N

Net force = 7.07 - 5 = 2.07 N in -x direction

Deaccleration

Velocity will decrease

In case B

velocity = 2 m/sec

in case C

force in +x direction = 0 N

force in -x direction = 0 N

Total force = 0

Force = m*a

accleration = 0 means speed is constant

speed = 2 m/sec

in case D:

force in +x direction = 10 N

force in -x direction = 10 N

Total force = 10 - 10 = 0

Force = m*a

accleration = 0 means speed is constant

speed = 2 m/sec

in case E:

force in +x direction = 10 N

Fx+ = 10 N

force in -x direction = 5*cos 45 deg + 5*cos 45 deg

Fx- = 7.07 N

Total force = 10 - 7.07 = 2.93 N

Force = m*a

accleration

means speed will increase.

in case F:

force in +x direction = 10 N

force in -x direction = 0 N

Total force = 10 - 0 = 10

Force = m*a

force is greater than the force in case E, so accleration will be higher

accleration

speed will increase also faster than case E

Order of their speed will be

F > E > B = C = D > A