Question

A 8-N block slides along a level surface. it has the inital speed of 7m/s. The work done by a 15N force pushing this block is: a) 3J
b) 6J
c) 56J
D) impossible to calculate without more information
e) none of these

Answer 1

Answer:

D) impossible to calculate without more information

Explanation:

Work (W) is defined as the product of the force (F) applied by the distance (d) the block moves.

The force involved in calculating this work must be parallel to the displacement, in this case it is the 15 N force.

W= F*d

W= 15*d

To calculate the distance (d) we have the equations the kinematic equations, they tell us that the block starts with initial velocity, then it is a uniformly accelerated movement, whose formulas are as follows:

vf²=v₀²+2*a*d Formula (1)

d= v₀t+ (1/2)*a*t² Formula (3)

Where:  

d:displacement in meters (m)  

t : time in seconds (s)

v₀: initial speed in m/s  

vf: final speed in m/s  

a: acceleration in m/s²

In formula (1) there are 3 unknowns (d,vf ,a)

In formula (2) there are 3 unknowns (d, t, a)

The coefficient of friction is unknown, and for this reason the acceleration cannot be calculated by applying Newton's second law.