解下到力學問題

Question

A toy car of mass 0.5kg runs freely down a smooth plane inclined at 30度 to the horizontal.

(a)What is the component of the car's weight along the plane?

(b) Hencefind the acceleration of the car.

(c) How long would it take the car to a distance of 1m along the plane?

(d) Now if a boy pulls the car upwards along the plane with a firce of 5N ,what would be the acceleration of the car?

Answer 1

(a) the weight component along the plane = 0.5g.sin(30) N = 2.5 N

(b) acceleration = force/mass = 2.5/0.5 m/s2 = 5m/s2

(c) u =0 m/s, a = 5 m/s2, s=1m, t=?
use s=ut+(1/2).at^2
1 = (1/2)(5)t^2
thus t = 0.63 s

(d) net force = (5-2.5) N = 2.5 N
acceleration = froce/mass = 2.5/0.5 m/s2 = 5 m/s2