Answer
(a) The two forces which are equal and opposite because of Newton's third law are the force of the bike pulling up on the Earth and the force of the Earth pulling down on the bike.
(b) The two forces which are equal and opposite because of Newton's first law are the force of the hook pulling up on the bike and the force of the Earth pulling down on the bike.
Work Step by Step
(a) According to Newton's third law, every force has an equal and opposite partner force. The two forces which are equal and opposite because of Newton's third law are the force of the bike pulling up on the Earth and the force of the Earth pulling down on the bike.
(b) The bike is in equilibrium so it does not accelerate. Therefore, according to Newton's first law, the net force on the bike is zero. The two forces which are equal and opposite because of Newton's first law are the force of the hook pulling up on the bike and the force of the Earth pulling down on the bike.
