2.4 Mechanics

Question 1

Describe the conditions needed for an object to be in an equilibrium state.

Answer 1

For an object to be in equilibrium, the sum of the forces in any direction must be at zero, AND the sum of all torques at any point must also be zero.

Question 2

Describe and explain the motion of a projectile.

Answer 2

• The only force acting on the projectile will be gravity vertically downwards.
• The projectile will decelerate until it reaches its maximum height, where its SPEED will be 0, and will then accelerate downwards until it hits the ground.
• The projectile will follow a parabolic path.
• The projectile’s horizontal speed also remains constant, as there are NO horizontal forces acting.

Question 3

What is the equation to calculate the velocity of an object in circular motion?

Answer 3

V= 2πr/t (π = pi, r = radius, t = time)

Question 4

What happens to an object in a circular motion if the centripetal force is reduced?

Answer 4

• The new centripetal force will not be sufficient to keep the object moving in a circle with the same radius.
• The radius of the circle the object moves in will decrease.
• The string holding the object will be angled more downwards.

Question 5

What happens when a car encounters an oil slick while turning?

Answer 5

• When a car is turning, centripetal force is the only force acting on the car.
• It comes from the friction force of the car’s tires on the road.
• The force acts towards the centre, therefore the car is constantly accelerating towards the centre.
• The oil slick means there is no friction, and therefore no centripetal force, and no circular motion.
• The car can’t turn and accelerate inwards, so it will keep moving at a tangent to the circle.
• It will move off of the road and crash.

Question 6

When calculating the torque for a bench, what assumptions can you make?

Answer 6

1: That the bench is uniform, so its weight force acts THROUGH its centre.
2: We assume that Tc =Tac for the bench to be in equilibrium.