Class Worksheet 3.1_Answer Forces and Newton s 1 st Law. Name: ( ) Date:

Size: px

Start display at page:

Download "Class Worksheet 3.1_Answer Forces and Newton s 1 st Law. Name: ( ) Date:"

Kory Anthony
5 years ago
Views:

1 Class Worksheet 3.1_Answer Forces and Newton s 1 st Law Name: ( ) Date: Class: Sec 3/ Marks: Definition of a force: A force is defined as an influence which changes, or tries to change, the state of motion of a body or the shape or size of a body. The SI unit for force is the newton represented by N. Newton s First Law (Law of Inertia): A body continues in its state of rest or uniform motion in a straight line unless a resultant force acts on it. i. The inertia of a body is its tendency to continue with its state of rest or motion. ii. iii. The mass of a body is a measure of its inertia. Inertia is (present / absent) for bodies in weightless environments e.g. outer space. 1. Using your understanding of force, put a tick in the space at the end of the descriptions below if there is a (resultant) force acting on the body. (a) A communication satellite orbiting around the earth at a constant speed. (b) A train accelerating on a straight track. (c) A skateboard coming to a stop after being released with a push. (d) An irregular lump of plasticine after being moulded into a cylinder. (e) A space shuttle traveling in outer space with constant velocity. (f) A lift just starting to rise. (g) (h) A man standing with a sack of flour on his shoulder. A balloon being inflated.

2 2. Explain the following using Newton s First Law. a) When a roller-coaster initially traveling in a straight line at constant speed suddenly turns right, the people in front of you are seen to swing their bodies to the left of their seats. When the roller-coaster suddenly turns right, the people will continue to move in a straight line (as shown below) according to Newton s first law. Hence they appear to swing to the left of their seats When the roller coaster turned to the right, the passengers swing to the left relative to the final route of the roller coaster. The path the roller coaster would have travelled if it did not turn to the right Left Right people b) When standing in a bus, you move forward when the bus comes to a stop. By Newton s first law, the passenger will continue to move forward with constant speed in a straight line when the bus comes to a stop.

3 3. Explain what happens when a ball is thrown by an astronaut in outer space. When the ball is thrown by an astronaut in the outer space, it will acquire an initial velocity, V. As there is an absence of air resistance in the outer space, (vacuum), the ball will continue to travel in an uniform motion in a straight line, according to Newton s First Law of motion. 4. Explain where a person on a moving train lands when she jumps up in the aisle. [Assumptions made: the train is moving in a straight line and it is not Accelerating, the train is closed and there is an absence of a wind force acting on the person.] She will land on the same spot from which she jumped. Before jumping upward, she had a forward velocity, which is that of the train. When she jumped, she continue to move with the same forward velocity as the train according to Newton s first law of motion. Note: May also consider cases where the train accelerates or decelerates.

4 5. Predict what happens to the objects in the following situations. (a) Three forces of 10 N, 4 N and 6 N being applied on a box at rest on a table. 10 N 6 N 4 N State of Equilibrium: The box will remain at rest as the net force acting on the box is zero. (b) A force F applied on a box travelling at a constant velocity v to the right. v When the force is applied, the velocity of the box will start to decrease at a constant rate or it undergoes a constant deceleration. [If the force is continuously applied on the box, the box will eventually come to a rest momentarily before it accelerates in the opposite direction.] V / ms -1 F Time / s (c) An upward force equal to the weight of the object, applied on the object which was falling freely. F = W (d) A ship being towed T by two tugboats T applying forces shown, F 1 being greater than F 2. F 1 F 2 T W F 2 ship The net force acting on the object is zero. It will continue its downward motion at a uniform velocity (second part of the graph below). F resultant V / ms -1 F 1 a net = 0ms -2 a net = 10ms -2 Time / s The vector sum of the pair of forces will produce a resultant force. The ship will move with a constant acceleration (a = F/m) in the direction of the resultant force.

NEWTON S FIRST LAW OF MOTION. Law of Inertia

NEWTON S FIRST LAW OF MOTION. Law of Inertia NEWTON S FIRST LAW OF MOTION Law of Inertia An object at rest will remain at rest unless acted on by an unbalanced force. An object in motion continues in motion with the same speed and in the same direction