A constant force pushes a block along a horizontal frictionless surface. The block moves from rest through a fixed distance.

Question 1

A constant force pushes a block along a horizontal frictionless surface. The block moves from rest through a fixed distance.

What is the relationship between the final speed v of the block and its mass m?

Reference: Past Exam Paper – June 2017 Paper 13 Q16

Solution:

Answer: C.

v² = u² + 2as

Since the block moves from rest, u = 0.

v² = 2as

So, v² ∝ a

Since a constant force is applied, F = ma, giving a = F/m

So, acceleration a ∝ 1/m

Replacing the relationship a ∝ 1/m into the equation involving velocity,

v² ∝ 1 / m

v ∝ 1 / √m