PHYSICS MID TERM FORMULAS

MIDTERM REVIEW ANSWERS

EXAMPLE WORD PROBLEMS: PRACTICE
DRAWING PICTURES AND LISTING VARIABLES!!!!

Police find skid marks of 50
meters on a road from a car that has a maximum

deacceleration of -40 m/s2. Was
the car exceeding the 20 m/s speed limit?

How long did it take the car to
stop?

*D=50*

*A=-40*

*Vf=0*

*Vi=???, T=???*

*Vf ^{2}=Vi^{2} +
2 A D*

*Vi = sqrt( 2* 40 * 50)*

*Vi= 63.2 m/s yes,*

*Vf=Vi+AT T= 63.2/40 T=1.58 sec*

If an object is dropped from a tower and it hits the
river 20 seconds later, how high
is the tower?

*Vi=0, T=20, A=-9.8*

*D=ViT + ½ A T ^{2}*

*D=0-4.9 * (20) ^{2}*

*D=1960 m*

If a diver dives off of a platform
that is 20 meters above the pool with an upwards velocity of 0.5 meters per
second, what is the final velocity of the diver as he hits the water, and how
long till he hits the water?

*Vi = +0.5 , A= - 9.8 , D= -20*

*Vf ^{2}=Vi^{2} +
2 A D*

*Vf= sqrt ( .5 ^{2}
– 2 * -9.8 * -20 )*

*Vf=-19.8 m/s ,*

* *

*Vf=Vi+AT T= ( -19.8 - .5 )/-9.8 /40 ,
T=2.072 sec*

A 4500 kg car is traveling along a
surface with the coefficient of friction of 0.4 at a speed of 54 m/s . He sees
the light and slams on his brakes, locking the tires and skids to a halt....
What is the distance he travels before he halts?

*m=4500*

*W=mg= 4500*9.8=44100 N*

*FN=W=44100*

*Ff= .4 (44100)= 17640 N*

*Fnet=Fp-Ff = Ff = 17640 N*

*Fnet=ma*

*17640 = 4500 a*

*a= -3.92*

*Vi= 54*

*Vf=0*

*Vf ^{2}=Vi^{2} +
2 A D*

*0= 54 ^{2} +2 * -3.92 *
D*

*D=2916/7.84 = 371.94 m*

*D=371.94 m*

An arrow is shot in the air with a
velocity of 61 meters per second at an angle of 20 degrees. How high will the
arrow go?

*Dy=22.2 m*

*Vx = 61 cos 20 =57.32*

*Dx=VxT*

* *

*Viy=61sin20=20.86*

*A=-9.8*

*At top Vfy=0*

*Vfy=Viy+AyT*

*0 = 20.86 -9.8*T*

*T=2.13 sec*

* *

*Vf ^{2}=Vi^{2} +
2 A D*

*0= 20.86 ^{2} +2 * -9.8
* D*

*D=435.27/19.6 = 22.2 m*

* *

A truck is stopped at a stoplight.
When the light turns green, it accelerates at 2 m/s 2 . At the same instant, a
car passes the truck going 30 m/s. Where and when does the truck catch up with
the car? draw the
accuarate distance time and velocity time graph

*Truck, vi=0, A = 2*

*D=ViT+1/2 A T ^{2}*

*D= ½*2*T ^{2}*

* *

*Car, A=0, Vi=30*

*D=30T*

* *

*So car=truck*

*30T=1T ^{2}*

*T=30, D=30*30=900m*

*T=30 sec, D=900 m*

What is the mass of a brick that I need 800 Newtons of force
to lift upwards and accelerate at 2 m/s/s ?

*Fnet=mA=Fup-W*

*ma=Fup-mg*

*m(2)=800-m(9,8)*

*m(11.8)=800*

*m=800/11.8=67.8 kg*

* *

A 50 Kg block sits on a 45 degree ramp and starts sliding
down. If the ramp has a coefficient of friction of .5, what acceleration does
the block have as it slides down the ramp?

*M=50*

*W=50*9.8=490*

*FN=490cos45=346.48 N*

*Ff= .5 (346.48) =173.24 N*

*Fp=490sin45=346.48 N*

*Fnet=Fp-Ff = 346.38
-173.24=173.24 N*

*Fnet=ma*

*173.24 = 50 a*

*A=3.465 m/s2*

* *