Mechanics | Relativity Answers

If a car moves round a circular road of radius r at a constant speed v, (A) its velocity changes and the acceleration is v/r^2 (B) there is no force on the car since its speed is constant (C) there is no velocity change since the speed is constant (D) the force on the car is towards the center and is mv^2/r (E) the force on the car is outwards from the center and is v^2/r.

If a car moves round a circular road of radius r at a constant speed v, (A) its velocity changes and the acceleration is v/r^2 (B) there is no force on the car since its speed is constant (C) there is no velocity change since the speed is constant (D) the force on the car is towards the center and is mv^2/r (E) the force on the car is outwards from the center and is v^2/r.

During the time between a parachutist leaving a plane and reaching the ground safely
1 the sum of her gravitational potential energy and her kinetic energy is constant
2 her kinetic energy depends upon her velocity
3 her gravitational potential energy is proportional to her height above the ground
Which of A, B, C, D, E shows the correct answers?
A 1, 2., 3 B 1, 2 C 2, 3 D 1 only E 3 only
Explain the reasons for your choice

A constant force F acts on a truck over a distance s and for a time t. The momentum gained by the truck is?

Multiple Choice Question
If a moving car X collides head-on with a moving car Y in the opposite direction, the conservation of momentum states (A) the final momentum of X = the final momentum of Y (B) the total momentum of X and Y is reversed by the collision (C) the total momentum of X and Y stays constant (D) the initial and final momentum of X is the same (E) the initial and final momentum of Y is the same

12 passengers per minute on average move on to an elevator (lift) which is rising steadily at 2m/s. Assuming the initial velocity of the passengers is zero, calculate the extra tension (force) due to the passengers on the belt round the elevator rollers. Average passenger mass = 60 kg.

A rocket is propelled by the emission of hot gases. It may be stated that both the rocket and the emitted hot gases each gain kinetic energy and momentum during the firing of the rocket. Discuss the significance of this statement in relation to the laws of conservation of energy and momentum, explaining the essential difference between these two quantities.

State Newton’s laws of motion. Explain how the “newton” is defined from these laws.

A hose directs a horizontal jet of water, moving with a velocity of 20m/s, on to a vertical wall. The cross-sectional area of the jet is 5 x 10-4m2. If the density of water is 1000kg/m^3, calculate the force on the wall assuming the water is brought to rest there.

The mass of a gas emitted from the rear of a toy rocket is initially 0.1kg/s. If the speed of the gas relative to the rocket is 50m/s, and the mass of the rocket is 2 kg, what is the initial acceleration of the rocket?