Practice Midterm 2
Problem 1
An electric vehicle starts from rest and accelerates at a rate of 2.0 m/s2 in a straight line
until it reaches a speed of 20 m/s. The vehicle then slows at a constant rate of 1.0 m/s2
until it stops. (a) How much time elapses from start to stop? (b) How far does the vehicle
travel from start to stop? (Answer: 30 s, 300 m)
Problem 2
A small ball rolls horizontally off the edge of a tabletop that is 1.20 m high. It strikes the
floor at a point 1.52 m horizontally from the table edge. (a) How long is the ball in the
air? (b) What is its speed at the instant it leaves the table? (Answer: 0.495 s, 3.07 m/s)
Problem 3
A block of mass 5.00 kg is pulled along a horizontal frictionless floor by a cord that
exerts a force of 12.0 N at an angle of 250 above the horizontal. (a) What is the block's
acceleration? (b) What is the force of the floor? (Answer: 2.18 m/s2, 43.9 N)
Problem 4
A 200 g ball is dropped from a height of 2.0 m and reaches a speed
of 6.3 m/s, and then bounces on a hard floor. The force on the ball
from the floor is shown in the figure. How fast is the ball moving after
bouncing from the floor?
Hint: Impulse = Fmax∙∆t/2. (Answer: 3.8 m/s)
Problem 5
A single frictionless roller-coaster car of mass 825 kg tops the first hill with speed 17.0
m/s at height 42.0 m. (a) What is the speed of the car at point B? (b) How high will the
car go on the last hill, which is too high for it to cross? (Answer: 0.53 J )
Problem 6
Use short concise sentences to answer the following questions using physics principles.
Make sure to explain your reasoning for each answer
a. Can an object be increasing in speed as its acceleration decreases? If so, give an
example and draw the motion diagram.
b. A cart rolling at constant velocity fires a ball straight up. When the ball comes
down will it land in front of the lunching tube, behind the launching tube, or
directly in it?
c. Why does a child in a wagon seem to fall backward when you give the wagon a
sharp pull?
d. Why, when you release an inflated, untied balloon, does it fly across the room?
e. Why is it tiring to push hard against a solid wall even though no work is done?
x
ax
vx
v0x
t
―
X
X
X
X
v x  v x 0  2ax x
X
X
X
X
―
x  v x 0 t  ax t
X
X
―
X
X
X
―
X
X
X
Kinematics
∆x a
vx
v0x t
v x  v x 0  ax t
2
∆y a
−g
vy
v0y t
2
1
2
2
x  (v x  v x 0 )t
1
2
A x  A cos 
A y  A sin 
x vx = vox t
A
A 2x  A 2y
y vy voy t
X
vy
voy
t
v y  v0y  gt
―
X
X
X
v  v  2gΔy
X
X
X
―
Δy  v0y t  gt
X
―
X
X
X
X
X
X
2
0y
2
Δy  (v y  v0y )t
1
2
FBC  FCB
p  J  Favg t  21 Fmax t
area under the curve
X
y
1
2
p  mv
Ax
y-Kinematics
2
y
Fy  may
Ay
x-Kinematics x vx = vox t
Δx  v0x t  v x t X
Fx  max
tan  
Fg  mg
fs,max  μsN
fk  μkN
p0  pf  J (momentum not conserved, J  0)

 
(momentum is conserved, J  0)
p0  pf
p10  p20  p1f  p2f 

m1v10  m2v 20  m1v1f  m2v 2f 
W  F  d  Fdcosθ
Emec  K1  U1  K 2  U2
W  E  (K, Ug, Eth )
E1  E2  Eth
K  21 mv 2 , Ug  mgy, Eth  fk x
P
E W

 Fv
t t