Phys101
Term: 122
Online HW-Ch05-Lec02
Q1:
Two equal forces act on isolated bodies A and B. The mass of B is two times that of
A. The magnitude of the acceleration of A is:
A.
B.
C.
D.
E.
double that of B
1/2 that of B
the same as B
four times that of B
1/4 that of B
Ans:
𝐀
Q2:
As shown in the figure, a 25 kg box is pushed across a frictionless horizontal floor
with a force F of magnitude 40 N, directed at an angle of 20 degrees below the
horizontal. Find the magnitude of the acceleration (in m/s2) of the box. (Give your
answer in three significant figures form)
Ans:
�⃗net = ma�⃗
Newton′ s 2nd Law: F
Along x − axis: Fx = ma ⇒ a =
Fx
m
Where Fx = F cos 20 = 40 cos 20 = 37.59 N
So: a =
37.59
= 1.50 m/s 2
25
KFUPM-Physics Department
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Phys101
Term: 122
Online HW-Ch05-Lec02
Q3:
In the system shown in the figure, a horizontal force acts on the 8.0 kg object. The
horizontal surface is frictionless and the pulley is ideal. Find the magnitude of F (in
N) if the 5.0 kg object has a downward acceleration of 1.0 m/s2? (Give your answer in
three significant figures form)
Ans:
From Newton’s 2nd Law; we consider the 2 kg and 5 kg blocks as one object of mass
7 kg.
* 8 kg block:
F − T = − 8 × a → (1)
* 7 kg block:
T − 7 × g = − 7 × a → (2)
Adding equation (1) and (2) we get:
F − 7 × 9.8 = − 8a − 7a
F = −15 a + 7 × 9.8 = 53.6 N
KFUPM-Physics Department
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