Phys101
Term:131
Online HW-Ch13-Lec02
Q1:
Neglecting air resistance, a 1.0-kg projectile has an escape velocity of about 11km/s at
the surface of Earth. The corresponding escape velocity for a 2.0kg projectile is:
Ans:
Escape Veolocity is independent to mass.
Q2:
An object is dropped from an altitude of one Earth radius above Earth's surface. If M
is the mass of Earth and R is its radius the speed of the object just before it hits Earth
is given by:
Ans:
K0 = 0
GMm
U0 = −
2R
1
K = mv 2
2
U=
i
R
f
R
−GMm
R
∆E = 0
∆K + ∆U = 0
K − K 0 + U − U0 = 0
1
GMm GMm
mv 2 − 0 −
+
=0
2
R
2R
GM
V= �
R
KFUPM-Physics Department
1
Phys101
Term:131
Online HW-Ch13-Lec02
Q3:
Two particles, each of mass m, are a distance d apart. To bring a third particle, with
mass 2m, from far away to a resting point midway between the two particles the work
done by an external agent is given by:
Ans:
m
m
d
m
U= −
Gm2
U0 = −
d
2m
d
2
m
d
2
Gm2 2Gm2 × 2 × 2
−
d
d
Gm2 8Gm2
= −
−
d
d
Wa = ∆U + ∆K
0
Wa = U − U0
Gm2 8Gm2 Gm2
=−
−
+
d
d
d
8Gm2
=−
d
KFUPM-Physics Department
2