You are riding a bicycle up a hill in a straight line at constant velocity The n

Question

You are riding a bicycle up a hill in a straight line at constant velocity The net force on you is (a) zero (b) forward (uphill) (c) backward (downhill) (d) toward the center of the Earth You press your physics textbook flat against a vertical wall with your hand What is the direction of the friction force exerted by the wall on the book. (a) downward (b) upward. (c) out of the wall (d) into the wall (e) that force does not exist. Extra point A car rounds an unbanked curve of radius r at constant speed v The required centripetal force is provided by (a) the weight of the car (b) the normal force exerted on the car (c) the force of kinetic friction between the tires and the road (d) the force of static friction between tires and road (e) the passengers in the car

Explanation / Answer

9) (d) The net force on you is towards center of the earth. on the cycle, the force applied will be in upward direction and the frictional force will be in downward direction.

10) (b) Frictional force always acts parallel to the surface and in opposite direction of motion. Here, in absence of friction, book will fall down, because of gravity acting on it The friction force acts opposite to the gravitational force on the book to keep the book in equilibrium. Because the gravitational force is downward, the friction force must be upward.

11 (d) The weight mg of the car acting vertically down is balanced by the normal reaction R of the ground.

Centripetal force acting on the car is provided by the force of static friction between the car tyre and the road.

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