PHY101 Assignment 1 - Solution

Q # 1: Consider a box that is placed on different surfaces. Marks = 10

a) In which situation (s) is there no force acting on the box?
b) In which situation (s) is there a static friction force acting on the box?
c) In which situation (s) is there a kinetic friction force acting on the box?

Various possible situations are as under:

I. The box is at rest on a rough horizontal surface.

II. The box is at rest on a rough tilted surface.

III. The box is on the rough-surfaced flat bed of a truck- the truck is moving at a constant velocity on a straight, level road and the box remains in the same place in the middle of the truck bed.

IV. The box is on the rough-surfaced flat bed of a truck- the truck is speeding up on a straight, level road, and box remains in the same place in the middle of the truck bed.

V. The box is on the rough-surfaced flat bed of a truck- the truck is climbing a hill, and the box is sliding towards the back of the truck.
Q # 2 A spaceship is moving in the vacuum of outer space, far from any planet, when its engine dies. As a result, the spaceship slows down and stops. What does Newton‘s first law say about this event? Marks = 5

Solution:-

In this situation there are no forces acting on the spaceship, so according to Newton’s first law, it will not stop. It continues to move in a straight line with constant speed, some science fiction movies have made use of very accurate science; this was not one of them.


Q # 3: A traffic light of weight W hangs from two light cables; one on each side of the light. Each cable hangs at a 450 angle from the horizontal. What I the tension in each cable? Marks = 5