Question

While Bob is demonstrating the gravitational force on falling objects to his class, he drops an 1.0 lb bag of feathers from the top of the science building. Determine the distance the bag has traveled after falling for 1.5 seconds assuming it has reach free fall and given the gravitational acceleration of 9.8 m/sec2.
A) 7.4 m
B) 11 m
C) 15 m
D) 22 m

Answer 1

the distance was 11 m

Answer 2

As per the question the mass of the bag of feathers is given as 1.0 lb.

Hence mass(m) = 1.0 lb

The bag is under free fall.Hence the acceleration with which the bag falls towards the centre of Earth is nothing else except the acceleration due to gravity.

Hence acceleration a=g=9.8 m/s^2

The time(t)given in the question=1.5 s

We are asked to calculate the distance travelled by the bag at that instant.

Let the air resistance is very small which is neglected.

From equation of kinematics we know that-

       S=ut +0.5at^2

Here S is the distance travelled,u is the initial velocity and a is the acceleration.

As the motion is under free fall,the initial velocity (u)= 0

Hence distance travelled

                S= 0×1.5+{0.5×(-9.8)×(1.5)^2}

                  =0-11.025 m

                  = -11.025 m

                  =  -11.0 m

Here negative sign only indicates vertical downward motion .

Taking only magnitude the distance travelled S =11 m.

Hence the correct option is B.