Question

Hilda pushes her sofa across the room with a force of 40 N. It accelerates at 2 m/s/s. What is the mass of the sofa?

Answer 1

The correct answer of this question is : A) 20 Kg and B) 3 seconds.

EXPLANATION :

As per the first question, the force applied on sofa F = 40 N.

The acceleration of the sofa a = $2\ m/s^2$.

We are asked to calculate the mass of the sofa.

From Newton's second law, we know that external unbalanced force is equal to the product of mass with acceleration of the body.

Mathematically force F = ma.

Hence, mass of the sofa is calculated as -

                              mass of sofa  m = $\frac{F}{a}$

                                                         = $\frac{40}{2}\ Kg$

                                                         = 20 Kg.

As per the second question, initial velocity u = 2 m/s due west.

The final velocity of the skateboard v = 8 m/s.

The acceleration of the skate board a = $2\ m/s^2$

The time taken [ t ] to reach that velocity is calculated as -

From equation of kinematics, we know that -

                                           v = u + at

                                          ⇒8 = 2 + 2t

                                         ⇒ 2t = 6

                                         ⇒  t = $\frac{6}{2}\ s$

                                           ⇒t = 3 s.            [ans]

                                                     

Answer 2

The first answer to the first question is 20 kg
the second answer to the second question is 3 seconds