Phys101
Term:131
Online HW-Ch06-Lec02
Q1:
The driver of a 1000-kg car tries to turn through a circle of radius
100m on an unbanked curve at a speed of 10m/s. The actual
frictional force between the tires and slippery road has a magnitude
of 900 N. The car:
A.
B.
C.
D.
E.
slides into the inside of the curve
makes the turn
slows down due to the frictional force
makes the turn only if it goes faster
slides off to the outside of the curve
Ans:
(fs = 900N) < (𝑚
E
v2
= 1000N)
r
Q2:
A 0.2-kg stone is attached to a string and swung in a circle of radius 0.6m on
a horizontal and frictionless surface. If the stone makes 150 revolutions per
minute, the tension force of the string on the stone is:
Ans:
150 rev → 1min(60sec) Then 1 rev → 0.4 sec
Period =
2πr
2πr
→v=
= 3πm/s
v
Period
mv 2 0.2 ∗ (3π)2
T=
=
= 29.9N
r
0.6
Q3:
At what angle should the roadway on a curve with a 50 m radius be banked to allow
cars to negotiate the curve at 12m/s even if the roadway is icy
Ans:
𝒚 − 𝒂𝒙𝒊𝒔 → 𝐹𝑁 𝑐𝑜𝑠𝜃 = 𝑚𝑔 … … . (1)
𝑣2
𝒙 − 𝒂𝒙𝒊𝒔 → 𝐹𝑁 𝑠𝑖𝑛𝜃 = 𝑚 … … . (2)
𝑅
Divide 2 and 1
𝑣2
𝑣2
𝑡𝑎𝑛𝜃 = 𝑔𝑅 → 𝜃 = tan−1 �𝑔𝑅� = 16.4𝑜
FN
FN sinθ
θ
FN cosθ
θ
mg
KFUPM-Physics Department
1