Question

A 700(N) boy at rest on in-line skates pushes a wall with a force of 300(N). There is a friction force of 70(N)

1. Name the external forces on the wall.

2. What is the accleration of the person

3. What will be the velocity of the person after 3(s). What will be the direction?

Answer 1

Answer:

1. The external forces are -

• Force exerted by the boy = 300 N
• Frictional force = 70 N

2. To calculate the accleration of the person, we can use Newton's second law of motion i.e F = ma

Where : F is net force , m is mass and a is acceleration

Net force can calculated by ,

• Net force = Force exerted by the boy - Frictional force
• Net force = 300 N - 70 N
• Net force = 230 N

Calculating the acceleration :

• a = F/m
• The mass of the boy is 700 N
• a = 230/700
• a = 0.33 m/s^2

3) The velocity of the person after 3(s) :

Using kinematics equation

• v = u + at

Here,

• v is final velocity
• u is initial velocity (0 m/s, because the boy is initially at rest )
• a is acceleration and
• t is time taken.

Plugging the required values -

• v = 0 + 0.33(3)
• v = 0.99 m/s

Hence, the velocity of the person after 3 seconds is 0.99 m/s.

The direction of the velocity will be towards the wall.