1.Two Liberty football players are running north down a football field in single

Question

1.Two Liberty football players are running north down a football field in single file. If the first player is moving at 8 m/s and the second is running at 10 m/s, how fast and in what direction will they be moving if player two crashes into player 1?

2. What if the people in the above problem had been running toward each other?

3. We are interested in looking at the effects of three muscles that cross the elbow…the pronator teres (PT), the flexor digitorum superficialis (FDS), and the Palmaris longus (PL). PT crosses the joint at 25 deg. and exerts a force of 40 N. FDS crosses the joint at 104 deg. and exerts a force of 55 N. PL crosses the joint at 86 deg. and exerts a force of 35 N. What total force can these three muscles exert together to cause elbow flexion?

Explanation / Answer

1. as no other infomration is provided, I will assume that it will be an inelastic collision and the two foorballers will

be moving together.

and also as their mass is not provided, lets assume both have same mass m kg.

then using conservation of momentum principle:

let final speed of combination of player 1 and 2 is v.

then m*8+m*10=m*v+m*v

==> v=9 m/s

Q2. if they are running towards each other, the net momentum will be along the direction of movement of

the second player.

considering that direction as +ve,

m*10-m*8=(m+m)*v

==> v=1 m/s

hence they will move with 1m/s speed along the direction of original direction of movement of second player.

Q3.

let the angle are with respect to x axis.

and the other axis is y axis.

then force exerted by PT:

force along x axis=40*cos(25)=36.25 N

force along y axis=16.904 N

force exerted by FDS:

force along x axis=55*cos(104)=-13.305 N

force along y axis=55*sin(104)=53.366 N

force exerted by PL:

force along x axis=35*cos(86)=2.44 N

force along y axis=35*sin(86)=34.91 N

hence net force along x axis=36.25-13.305+2.44=25.385 N

net force along y axis=16.904+53.366+34.91=105.18 N

angle with x axis=arctan(y component/ x component)=arctan(105.18/25.385)=76.43 degrees

net force magnitude=sqrt(25.385^2+105.18^2)=108.2 N

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