Question

1. why should an iron almirah be called solid?

three marks questions :
. a truck starts from rest and rolls down a hill with a constant acceleration. it travels a distance of 400 m in 20 s. find its acceleration. find the force acting on it if its mass is 7 tonnes. (1 tonne = 1000kg)
. derive the formula of force using newton law of motion.
. differentiate between plant cell and animal cell.
. differentiate between colloidal and suspensions.
.differentiate between distance and displacement.
. a train is travelling at a speed of 90 km/h brakes are applied so as to produce a uniform acceleration

Explanation:

1. Why should an iron almirah be called solid?

An iron almirah has definite shape and volume. Its particles are closely packed with strong intermolecular forces, characteristic of solids.

Step1: Use the second - equation of motion

The second - equation of motion is $s = ut+\frac{1}{2}at^{2}$. Since the truck starts from rest, $u = 0$. The equation becomes $s=\frac{1}{2}at^{2}$. We need to solve for $a$.
$s = 400m$, $t = 20s$. Rearranging for $a$, we get $a=\frac{2s}{t^{2}}$.
$a=\frac{2\times400}{20^{2}}$

Step2: Calculate the acceleration

$a=\frac{800}{400}=2m/s^{2}$

Step3: Calculate the mass in kg

The mass of the truck $m = 7$ tonnes. Since 1 tonne = 1000 kg, $m=7\times1000 = 7000kg$

Step4: Use Newton's second law to find the force

Newton's second law is $F = ma$. Substituting $m = 7000kg$ and $a = 2m/s^{2}$, we get $F=7000\times2$
$F = 14000N$

Step1: State Newton's second law

Newton's second law states that the rate of change of momentum of a body is directly proportional to the applied force and takes place in the direction in which the force acts.
Momentum $p=mv$, where $m$ is the mass and $v$ is the velocity.
The rate of change of momentum $\frac{\Delta p}{\Delta t}=\frac{p_{2}-p_{1}}{t_{2}-t_{1}}$
If the mass $m$ is constant, $p_{2}=mv_{2}$ and $p_{1}=mv_{1}$
So, $\frac{\Delta p}{\Delta t}=\frac{mv_{2}-mv_{1}}{t_{2}-t_{1}}=m\frac{v_{2}-v_{1}}{t_{2}-t_{1}}$

Step2: Recall the formula for acceleration

We know that acceleration $a=\frac{v_{2}-v_{1}}{t_{2}-t_{1}}$

Step3: Obtain the force formula

Since $\frac{\Delta p}{\Delta t}\propto F$ and $\frac{\Delta p}{\Delta t}=ma$, and taking the proportionality constant as 1 (in SI units), we get $F = ma$

Answer:

An iron almirah is called solid because it has a definite shape and volume, and its particles are closely - packed with strong intermolecular forces.

2. A truck starts from rest and rolls down a hill with a constant acceleration. It travels a distance of 400 m in 20 s. Find its acceleration. Find the force acting on it if its mass is 7 tonnes. (1 tonne = 1000 kg)