#### 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. Additional Problems