#### Transcript Ch-5

```Newton's first law of motion - sometimes referred to as the law of
inertia. An object at rest stays at rest and an object in motion stays
in motion with the same speed and in the same direction unless
acted upon by an unbalanced force.
A force is a push or pull upon an object resulting from the object's
interaction with another object.
Newton (N), F=ma
1N= (1kgx1m/s2)
“an inertial frame is one that is not accelerating”.
c, d and e
mass, in physics, the quantity of matter in a body regardless of its volume or of any forces acting on it. The term
should not be confused with weight, which is the measure of the force of gravity acting on a body.
OR
Mass is the quantity of inertia possessed by an object or the proportion between force and acceleration referred to
in Newton's Second Law of Motion.
(a) and (b) 2N leftward, there will be no acceleration in either
case
Section C is two dimensional problem
Free Fall
(a) Equal (b) greater, because the acceleration is upward, therefore
normal force must be upward.
Friction is the force that opposes the motion of an object.
Tension is a force that stretches something. Tensional force is a
force applied by an object being stretched. The object being
stretched might be a rope, a string or a wire. The tensional force
of the object is applied on the objects that are stretching it.
Tensional force is directed along the stretched object. It pulls
equally on the objects on either end of the rope or the elastic
band that is being stretched.
(a) equal, (b) grater and (c) less
T3=mDg, mD=T3/g=9.8/9.8=1 kg
T2=(mD+mC)g, mC=4kg
T1=(mD+mC+mB)g, mB=1kg
(a) increase, (b) yes, (c) same , (d) yes
Since the sled is at rest, therefore sum of all forces must be
equal to zero,
Question 1: A 8 Kg mass is hanging at the end of a string. Find the tension in the string if
acceleration of the mass is (a) 3 m/s2 in the upward direction (b) 3 m/s2 in downward direction.
Solution:
Given: Mass of the hanging body m = 8 Kg,
(a) If the body is moving in upward direction the tension force is given as
T = mg + ma = 8 × 9.8 + 8 × 1.5 = 90.4 N
(b) If the body is moving in down direction the tension force is given as
T = mg - ma = 8 ×9.8 - 8 × 1.5 = 66.4 N.
Question 2: A 500 N man stands on the floor of an elevator. The scale is recording the force. what will be
the force if the acceleration is (a) 1.5 m/s2 in upward direction (b) 9.8 m/s2 in downward direction.
Solution:
Given: Weight of the man W = 500 N,
∴ Mass of man is m = W/g = 500/9.8 = 51.02 Kg.
(a) If the body is moving in upward direction the tension force is given as
T = W + ma = 500 + 51 × 1.5 = 500 +76.5 = 576.5 N
(b) If the body is moving in down direction the tension force is given as
T = W - ma = 500 - 51.02 ×× 9.8 = 500 N - 499.998N = 0 N.