Physics Answers

A train has a max speed of 20m/s w/c it can achieve at an acceleration of 0.25m/s². With its brake fully applied, the train has a deceleration of 0.5m/s². What’s the shortest time that the train can travel b/w stations 8k m apart if it stops at both?

An electric train develops a power of 1.0 MW when travelling at a constant speed of 50 ms-1. The net resistive force acting on the train is (Ans: 20 kN).

My work: P=FV, F=P/V, F=2x10^-6

A machine lifts an object of weight 1.5 x 103 N to a height of 10 m. The machine has an overall efficiency of 20%. The work done by the machine in raising the object is: (Ans: D)

A. 3.0 x 103 J

B. 1.2 x 104 J

C. 1.8 x 104 J

D. 7.5 x 104 J 

Which one of the following objects is in equilibrium? (Could someone give reasoning on the answer?)

A. A stone trapped in the tread of a rotating tyre. B. An air molecule as a sound wave passes through the air. C. A steel ball falling at constant speed through oil. D. An electron moving through a metal under the action of a potential difference.

Ans from sheet: D

a 0.40-kilogram mass is sliding on a horizontal friction less air track with a speed of 6.0 meters per second when it instantaneously hits and sticks to a 2.6-kilogram mass initially at rest on the track. The 2.6-kilogram mass is connected to one end of a mass less spring, which has a spring constant of 200 newtons per meter. The other end of the spring is fixed.

Find the magnitude and direction of the vector represented by each of the following pairs of components:

(a) 𝐴𝑥 = 3.0 𝑐𝑚, 𝐴𝑦 = −4.0 𝑐𝑚;

(b) 𝐴𝑥 = −5.0 𝑚, 𝐴𝑦 = −12.0 𝑚;

(c) 𝐴𝑥 = −2.0 𝑘𝑚, 𝐴𝑦 = 3.0 𝑘𝑚.

The equation of motion:

r = -10i + 15t j + 5t2k

Q: (1)The average velocity from t=Is to t=2s

(2) The instantaneous velocity and acceleration at t=2s.

A tall fat and skinny girl athlete of mass 55 kg throws a ball of mass 0.80kg against a wall. The ball strikes the wall horizontally with a speed of 25m/s and it bounces back with the same speed. The ball is in contact with the wall 0.050s. Determine the magnitude of the average force exerted on the wall by the ball?

A certain traveling wave has frequency of 200hz. A wave length of 2m and an amplitude of 0.04m. calculate the displacement (Y) at a point (x) 0,3 from the origin at a time 0.01sec after zero displacement at that point (note, the wave is traveling in opposite direction).