A 1500 kg vehicle is traveling on a dry pavement where the coefficient of kineti

Question

A 1500 kg vehicle is traveling on a dry pavement where the coefficient of kinetic friction is 0.80. If the car is going at 25m/s, what minimum distance is required to stop the car when the brakes are locked?

a) 72 m

b) 64 m

c) 55 m

d) 40 m

e) None of the above

A 1500 kg automobile going on a smooth road at a constant speed of 16.0 m/s suddenly encounters high blowing winds. The air drag of the winds varies with the speed as F=-120vN where v is the speed in m/s. What is the speed of the vehicle after 10 s?

a) 16m/s

b) 14m/s

c) 9.6m/s

d) 7.2m/s

e) None of the above

A box is pulled across a horizontal floor at a constant speed by a 12N force applied by a rope at an angle of 23 degrees above the horizontal. The work done by the force of kinetic friction after moving the box 4.0 m is:

a)44 J

b)48 J

c)-44 J

d)-48 J

e)None of the above

A 5.0 kg ball thrown straight up, from the ground, with an initial speed of 30.0 m/s has its location with respect to the ground given by the height y(t)=30t - 12t^2 - 20t^3.

a)64 m

b)42 m

c)34 m

d)16 m

e)None of the above

Explanation / Answer

a)answer is d

force of friction = u m g
umg = ma
a = u g
v^2 = v0^2 + 2 a s
s = v0^2/2a = 25^2/(2*0.8*9.81)= 40

b)answer is d

F = ma

u know that a =dv/dt as derivative of velocity is accelaration

F=-120vN

a=dv/dt
-120 v = 1500* dv/dt
dv/v = -12/150 dt
ln v = -12/150 t + C
v = v0 e^(-12/150*t)
v = 16*e^(-12*10/150)

v=7.2

c)answer is c

At constant speed work done by the force and the work done by friction =0

Wf + Wfr =0
Wf = F d cos theta

Wf= 12*4*cos(23)=44
Wfr = -44 J

d)answer is e

At the maximum height potential energy is equal to zero

i.e dy/dt = 0

d/dt(30t - 12t^2 - 20t^3) = 0

30-24t -60t^2 =0

10-8t-20t^2=0

5 - 4t -10t^2 = 0

x1 = 4+root(16-(4*10*5))/20 =0.87823 h = 3.844

x2 = -4+root(16-(4*10*5))/20=0.47823 h =9.37274

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