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?
2 kg
20 kg
40 kg
80 kg

keiko is riding a skateboard 2 m/s, west. how long will it take her to reach a velocity of 8 m/s, west if her acceleration is 2 m/s2?
3 seconds
6 seconds
8 seconds
10 seconds

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 = .

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 =

                                                         =

                                                         = 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 =

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 =

                                           ⇒t = 3 s.            [ans]

weight of the box is given as

here this is placed on the inclined of angle 42 degree

now this weight will have two components one is along the incline other is perpendicular to it

so here we need to apply a force parallel to incline opposite to its component of weight

so here the component of weight is given as

here we have

so it requires 75 n force to move it upwards