Tag: introduction to simple machines

Questions Related to introduction to simple machines

When the same amount of force is applied :

  1. A nail travels more distance than a screw into the wood board

  2. Screw travels more distance than the nail

  3. Both pierce the wood board to equal distance

  4. None of the above


Correct Option: B

A boy can exert a maximum force of $10$kg, i.e he cannot lift vertically a load of mass more than $10$kg. Now if he wants to raise a load of mass $20$kg on to a high eall, he can do it with the help of an inclined place making an angle $\theta$ with the horizontal. Find $\theta$.

  1. $60^o$

  2. $80^o$

  3. $30^o$

  4. $20^o$


Correct Option: C
Explanation:

$sin \theta=\dfrac{1}{M.A}=\dfrac{Effort}{Load}=\dfrac{10}{20}=\dfrac{1}{2}$
Thus, by placing a wooden plank at $\theta=30^o$ an angle equal to $30^o$ with the horizontal group can push the load of mass $20$Kg at any height by exerting a force(or effort) of $10$kg.

The velocity ratio of a machine is 1 if 

  1. The displacement of load is equal to the displacement of effort

  2. The displacement of load > equal to the displacement of effort

  3. The displacement of load < equal to the displacement of effort

  4. None of the above 


Correct Option: A
Explanation:

The velocity ratio of a machine is equal to the displacement of effort such a machine changes the direction of effort.

As the closeness of threading increases in a screw :

  1. mechanical advantage decreases

  2. effort required will be less

  3. inclination increases

  4. all the above


Correct Option: B

It is harder to cut an apple with a butter knife, because :

  1. Butter knife has more inclination

  2. Mechanical advantage of butter knife is less

  3. It has a high angle of wedge

  4. All of the above


Correct Option: D

If a machine overcomes a load $L$ and the distance travelled by the load is $25 m$. Similarly, the effort applied in the machine is $E$ and the distance travelled by effort is $75 m$, and $'T'$ is the time taken,then velocity ratio is:

  1. $\dfrac{1}{3}$

  2. $\dfrac{2}{3}$

  3. $\dfrac{3}{1}$

  4. $1$


Correct Option: A
Explanation:
The VR is define as ratio of distance travelled by effort:distance travelled by load

$VR=\dfrac{{E}{} _{d}}{{L}{} _{d}}$


$VR=\dfrac{25}{75}$

$VR=\dfrac{1}{3}$

option A is correct.

A load will be lifted by an effort of 12 N, the velocity ratio is 18 and the efficiency of the machine at this load is 60%, if the machine has a constant frictional resistance, determine the law of machine.

  1. P = W/18 + 4.8

  2. P = W/8 + 6.4

  3. P = W/14 + 8.2

  4. none of these


Correct Option: A

In a simple machine, whose velocity ratio is $30$, a load of $2400$ N is lifted by an effort of $150$ N and a load of $3000$ N is lifted by an effort of $180$ N. Find the law of machine -

  1. $P = 0.50W + 144$

  2. $P = 0.60W + 25$

  3. $P = 0.05 W + 144$

  4. $P = 0.05 W + 30$


Correct Option: D

In a simple machine, whose velocity ratio is $30$, a load of $2400 N$ is lifted by an effort of $150$ N and a load of $3000$ N is lifted by an effort of $180$ N. Calculate the amount of effort wasted in overcoming the friction using a force of $200 N$. 

  1. 86.67N

  2. 58.25N

  3. 89.25N

  4. 89.89N


Correct Option: A

A machine gun is mounted on a 2000 kg car on a horizontal frictionless surface. At some instant, the gun fires 10 bullets/second, each of mass 10 g with a velocity of 500 m s$^{-1}$. The acceleration of the car is

  1. 0.025 ms$^{-2}$

  2. 0.25 ms$^{-2}$

  3. 0.5 ms$^{-2}$

  4. 500 ms$^{-2}$


Correct Option: A
Explanation:

$M _{car}=2000kg$


$n=10 \ bullets/s$

$M _{b}=10g=0.01kg$

$V _{b}=500m/s$

Momentum of each bullet $=0.01\times 500$

$(M _{b}V _{b})P _{b}=5kgm/s$

Force on car $=nP _{b}$

                       $50kgm/s^{2}$
$F _{car}=50N$

$a _{car}=\dfrac{50}{2000}=\dfrac{1}{40}$

$a _{car}=0.025m/s^{2}$